Version bump (gitlab 7.5.0 and gitlab-shell 2.3.1)
Rework secrets

Gitlab-shell will now change secrets on updates, which is fine since
only gitlab needs to know the secret. Both are patched to use the
same file (/etc/webapps/gitlab-shell/secret) instead of using symlinks.

Gitlab keeps a static secret file since that is exposed to clients.
It, too, is patched to take the secret from /etc/webapps/gitlab/secret
directly instead of using symlinks.