Merge branch 'fdroid-version' into 'master'

fdroid --version and shared tests between gitlab and jenkins

This adds a `fdroid --version` flag for people to easily see the exact version of fdroidserver in use.  It'll also report the version using `git describe` when running from git.

The other moves the extended tests out of `./jenkins-build` into a common script for both gitlab-ci and jenkins.

See merge request !70