Merge branch 'vis_btn_color_change' into 'master'

Changed the color of admin/application_settings buttons

Now they look like this: ![image](https://gitlab.com/gitlab-org/gitlab-ce/uploads/a43c0c7fada5768bddda6e3449b37a5e/image.png)

gray when selected, white when not.

See merge request !887

app/helpers/application_settings_helper.rb

@@ -28,7 +28,7 @@ module ApplicationSettingsHelper
   def restricted_level_checkboxes(help_block_id)
     Gitlab::VisibilityLevel.options.map do |name, level|
       checked = restricted_visibility_levels(true).include?(level)
-      css_class = 'btn btn-primary'
+      css_class = 'btn'
       css_class += ' active' if checked
       checkbox_name = 'application_setting[restricted_visibility_levels][]'