Fix: API 500 error when project does not exists

Fix overflow of text in the project summary box in Chrome and Safari

Merge pull request #3583 from karlhungus/update_dev_setup_to_not_use_hard_coded_path_to_gitlab_shell

Updated setup to reference the gitlab-shell var

Added os_name support for systems running systemd.

Added check_redis_version to check.rake

Fixed typo in gitlab.yml.example

contribution guidelines: no feature requests on the Github issue tracker

State clearly that the issue tracker is not used for feature requests
and link to http://feedback.gitlab.com.

Checking the redis version will warn users that
are using an old version to update. Included
reference to the troubleshooting guide.