Also converts doc/README.md to Unix line endings

This controller is now the target for `root_url`. It sub-classes
DashboardController so we can render the old default without a redirect
if the user hasn't customized their dashboard location.

It was only used for the appearance live updating, which is now handled
by Profiles::Preferences#update

Consolidates the helpers related to user preferences.

Renames `app_theme` to `user_application_theme` to better explain what
it is.

Now we can simply loop through all themes, among other things.

This also removes the `dark_theme` / `light_theme` classes and the
`theme_type` helper, since they weren't used anywhere.

Since they're all defined by a mixin, it didn't provide any benefit to
have them in separate files.

This also adds variables defining the basic color of each theme so we
can re-use them in the previews.

Ensure `session_expire_delay` field exists before accessing it

Closes #1798

See merge request !808

Closes #1798

Add info about regex anchors to shell command docs.

Addresses internal issue https://dev.gitlab.org/gitlab/gitlab-ee/issues/263.

See merge request !805

Add session expiration delay configuration through UI application

Setting is accessible by the administrator through the UI and defaults to 1 week (the current setting)

Answers the following suggestions:

  * http://feedback.gitlab.com/forums/176466-general/suggestions/6210719-make-session-length-configurable
  * http://feedback.gitlab.com/forums/176466-general/suggestions/6730512-automatic-logout-after-a-time-being-idle

See merge request !774

Add 7.12 update guides

See merge request !1858

Fix typo on account page.

@douwe Thanks for reviewing this small fix.

See merge request !1854

Update install docs for 7.12

See merge request !1857

Even though the 7-12-stable branch does not exist yet.

Git 2.1.2 does not protect against pushes trying the '.Git/config'
attack (CVE-2014-9390). Going to 2.4.3 is perhaps a big jump but why not
use the latest? (Famous last words.)

Remove text since rss is now to prominent.

See merge request !1855

Fix link to howto_rc1.md

The relative link that was there before breaks when you copy-paste the
issue template into an actual issue.

See merge request !1856