Gitlab CI: build & publish nightlies
I would like to test Usage and nightlies would be a good way to do so. This MR uses the CI template that builds and deploy a flatpak bundle available to download from Gitlab & the nightly repository. It also setups dual installation.
This replaces !41 (closed) and fixes few parts of #44 (closed)
Edited by Bilal Elmoussaoui