Improve F-Droid's repositories on GitLab

This isn't related to the client at all, it's more related to its, the server's and data's repository on GitLab.

I have some suggestions on the settings of the repositories of F-Droid.

All:

• Enable snippets to allow users (?) to share things like larger logcats,...
• Update/Add the application icon as the project avatar
• Enable the service "External Wiki" and link the wiki from f-droid.org

Client(/Server) only:

• Enable the service "Jenkins CI" to link Jenkins to this repo
• Enable the new feature "Approve MRs"