GitLab

Fixes: #138

Looks like this is still desynced with backend, however I will not touch
it until new frontend/backend pair will go live with all things fixed at
once

Fixes: #132

Fixes: #129

Thanks to Fabian Bräunlein for finding this issue.
Signed-off-by: Yuri Konotopov <ykonotopov@gnome.org>

See-Also: https://discourse.gnome.org/t/new-gnome-versioning-scheme/4235

Move build steps from Dockerfile to separate script. Run tests directly
in the image via regular GitLab pipeline.

Users have been discouraged from using the Reject action on their own
extensions for quite awhile. This disrupts the diff review flow since
new submissions need to be manually checked to ensure we don't miss
buggy/malicious in a version rejected by a user.

fixes #99