Gitlab sends multiple commits in the order reversed from Github. As this only broke recently, I suspect that they may have changed the ordering. This change makes the code order-agnostic to hopefully remove the problem going forward.
Fixes#1900
Gitlab will occasionally send trigger payloads with an empty commit list (and a null checkout_ha) for branches that have been deleted. Properly handle that case.
- Move each trigger handler into its own file
- Add dictionary helper classes for easier reading and writing of dict-based data
- Extract the web hook payload -> internal representation building for each trigger system
- Add tests for this transformation
- Remove support for Github archived-based building
