Respect the configured redis URL when initializing the session store

It was not possible to start Gitlab with a redis server running on another host or port. Every other subsystem that uses redis respects the settings in config/resque.yml.

This patch uses the configured url from the cache_store configuration.
The cache_store configuration already loads the correct redis url from config/resque.yml.

Closes #5406

Check if a file is editied "on" a branch or a commit.

The previous behavior was a "disabled" link, which was still clickable
and linked to the edit file action.

If the 	user accesses a path like "/edit/master/README" show the file
edit form (just like before).

If the user accesses a path like
"/edit/8d5c1f375ce99e5df84e26b0eafbf1448c6a001e/README", redirect the
user to the file detail page with a note, that he cannot edit a file
"on" a commit.

fixes #5482

Reset buttons/links on the reset password page

Update installation.md

Updated instructions to include proper stable. Otherwise they fail due to Rack extensions required below.

Fix for issue #5431

If you enable GitLab CI for project you will be able to clone project
source code with next command:
git clone http://gitlab-ci-token:XXXXXXXXXXXX@host:project.git
Requires for GitLab CI 4.0

Added git command to change shell to 1.1.0 to make sure the check passes

Non-logic wording and grammar for the new group view

Made stop message make more sense, app_root now uses the user name.