Upgrade to GitLab5.0 and its GitLab-shell project.

M .gitignore:
  Ignores '/gitlab/gitlab-shell'
M gitlab/gitlab.yml.tpl:
M gitlab/install_or_update_gitlab.sh.tpl:
  Install 'gitlab-shell', and calls it 'check' step.
A gitlab-shell:
  symlink to '/gitlab/gitlab-shell/'.
  Must be at the same level than '/repositories/'
A gitlab/config.yml.tpl:
  Add Gitlab-shell config