Merge branch 'system-font-test' into 'master'

Use system font

Just for fun....   
### macOS Chrome (San Francisco):   
![Screen_Shot_2016-11-17_at_4.01.29_PM](/uploads/bfbab440ea0136314a6a7cffcd44f3ff/Screen_Shot_2016-11-17_at_4.01.29_PM.png)
### macOS Safari (San Francisco):   
![Screen_Shot_2016-11-18_at_8.28.22_AM](/uploads/3adc05d7adf84ca726cbaaf36cb0567d/Screen_Shot_2016-11-18_at_8.28.22_AM.png)
#### Ubuntu Firefox (Ubuntu): 
![Screen_Shot_2016-11-18_at_8.31.08_AM](/uploads/0f0d581d2d79d5db3dba9b2200499dc7/Screen_Shot_2016-11-18_at_8.31.08_AM.png)
#### Windows 7 IE 11 (Segoe UI): 
![Screen_Shot_2016-11-18_at_8.35.05_AM](/uploads/88efc2c554252de03fb84cc3c3e2856e/Screen_Shot_2016-11-18_at_8.35.05_AM.png)

See merge request !7545

app/assets/fonts/OFL.txt

-Copyright 2010, 2012, 2014 Adobe Systems Incorporated (http://www.adobe.com/), with Reserved Font Name 'Source'. All Rights Reserved. Source is a trademark of Adobe Systems Incorporated in the United States and/or other countries.
-
-This Font Software is licensed under the SIL Open Font License, Version 1.1.
-
-This license is copied below, and is also available with a FAQ at: http://scripts.sil.org/OFL
-
-
------------------------------------------------------------
-SIL OPEN FONT LICENSE Version 1.1 - 26 February 2007
------------------------------------------------------------
-
-PREAMBLE
-The goals of the Open Font License (OFL) are to stimulate worldwide
-development of collaborative font projects, to support the font creation
-efforts of academic and linguistic communities, and to provide a free and
-open framework in which fonts may be shared and improved in partnership
-with others.
-
-The OFL allows the licensed fonts to be used, studied, modified and
-redistributed freely as long as they are not sold by themselves. The
-fonts, including any derivative works, can be bundled, embedded, 
-redistributed and/or sold with any software provided that any reserved
-names are not used by derivative works. The fonts and derivatives,
-however, cannot be released under any other type of license. The
-requirement for fonts to remain under this license does not apply
-to any document created using the fonts or their derivatives.
-
-DEFINITIONS
-"Font Software" refers to the set of files released by the Copyright
-Holder(s) under this license and clearly marked as such. This may
-include source files, build scripts and documentation.
-
-"Reserved Font Name" refers to any names specified as such after the
-copyright statement(s).
-
-"Original Version" refers to the collection of Font Software components as
-distributed by the Copyright Holder(s).
-
-"Modified Version" refers to any derivative made by adding to, deleting,
-or substituting -- in part or in whole -- any of the components of the
-Original Version, by changing formats or by porting the Font Software to a
-new environment.
-
-"Author" refers to any designer, engineer, programmer, technical
-writer or other person who contributed to the Font Software.
-
-PERMISSION & CONDITIONS
-Permission is hereby granted, free of charge, to any person obtaining
-a copy of the Font Software, to use, study, copy, merge, embed, modify,
-redistribute, and sell modified and unmodified copies of the Font
-Software, subject to the following conditions:
-
-1) Neither the Font Software nor any of its individual components,
-in Original or Modified Versions, may be sold by itself.
-
-2) Original or Modified Versions of the Font Software may be bundled,
-redistributed and/or sold with any software, provided that each copy
-contains the above copyright notice and this license. These can be
-included either as stand-alone text files, human-readable headers or
-in the appropriate machine-readable metadata fields within text or
-binary files as long as those fields can be easily viewed by the user.
-
-3) No Modified Version of the Font Software may use the Reserved Font
-Name(s) unless explicit written permission is granted by the corresponding
-Copyright Holder. This restriction only applies to the primary font name as
-presented to the users.
-
-4) The name(s) of the Copyright Holder(s) or the Author(s) of the Font
-Software shall not be used to promote, endorse or advertise any
-Modified Version, except to acknowledge the contribution(s) of the
-Copyright Holder(s) and the Author(s) or with their explicit written
-permission.
-
-5) The Font Software, modified or unmodified, in part or in whole,
-must be distributed entirely under this license, and must not be
-distributed under any other license. The requirement for fonts to
-remain under this license does not apply to any document created
-using the Font Software.
-
-TERMINATION
-This license becomes null and void if any of the above conditions are
-not met.
-
-DISCLAIMER
-THE FONT SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
-EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTIES OF
-MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT
-OF COPYRIGHT, PATENT, TRADEMARK, OR OTHER RIGHT. IN NO EVENT SHALL THE
-COPYRIGHT HOLDER BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
-INCLUDING ANY GENERAL, SPECIAL, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL
-DAMAGES, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
-FROM, OUT OF THE USE OR INABILITY TO USE THE FONT SOFTWARE OR FROM
-OTHER DEALINGS IN THE FONT SOFTWARE.

app/assets/stylesheets/framework.scss

-@import "framework/fonts";
 @import "framework/variables";
 @import "framework/mixins";
 @import 'framework/tw_bootstrap_variables';

app/assets/stylesheets/framework/fonts.scss

-// Disabling "SpaceAfterPropertyColon" linter because the linter doesn't like
-// the way the `src` property is formatted in this file.
-// scss-lint:disable SpaceAfterPropertyColon
-
-/* latin-ext */
-@font-face {
-  font-family: 'Source Sans Pro';
-  font-style: normal;
-  font-weight: 300;
-  src:
-    local('Source Sans Pro Light'),
-    local('SourceSansPro-Light'),
-    font-url('SourceSansPro-Light.ttf.woff2') format('woff2'),
-    font-url('SourceSansPro-Light.ttf.woff') format('woff');
-}
-@font-face {
-  font-family: 'Source Sans Pro';
-  font-style: normal;
-  font-weight: 400;
-  src:
-    local('Source Sans Pro'),
-    local('SourceSansPro-Regular'),
-    font-url('SourceSansPro-Regular.ttf.woff2') format('woff2'),
-    font-url('SourceSansPro-Regular.ttf.woff') format('woff');
-}
-@font-face {
-  font-family: 'Source Sans Pro';
-  font-style: normal;
-  font-weight: 600;
-  src:
-    local('Source Sans Pro Semibold'),
-    local('SourceSansPro-Semibold'),
-    font-url('SourceSansPro-Semibold.ttf.woff2') format('woff2'),
-    font-url('SourceSansPro-Semibold.ttf.woff') format('woff');
-}
-@font-face {
-  font-family: 'Source Sans Pro';
-  font-style: normal;
-  font-weight: 700;
-  src:
-    local('Source Sans Pro Bold'),
-    local('SourceSansPro-Bold'),
-    font-url('SourceSansPro-Bold.ttf.woff2') format('woff2'),
-    font-url('SourceSansPro-Bold.ttf.woff') format('woff');
-}

app/assets/stylesheets/framework/variables.scss

@@ -266,7 +266,7 @@ $diff-view-modes-border: #c1c1c1;
  * Fonts
  */
 $monospace_font: 'Menlo', 'Liberation Mono', 'Consolas', 'DejaVu Sans Mono', 'Ubuntu Mono', 'Courier New', 'andale mono', 'lucida console', monospace;
-$regular_font: 'Source Sans Pro', "Helvetica Neue", Helvetica, Arial, sans-serif;
+$regular_font: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen-Sans, Ubuntu, Cantarell, "Helvetica Neue", sans-serif;
 
 /*
 * Dropdowns