The big merge request for 3.30 Sdk

This is what I've been working on with @alatiera since gnome 3.30 was released.

There are multiple versions of the CI configuration used to push the code to gbm-builder. I didn't want to squash them together because there are merge requests against this branch, but I feel it would be cleaner to squash all the .gitlab-ci.yml changes into two or three commits.