Start refactoring of the trigger system:

- 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

endpoints/building.py

@@ -96,7 +96,7 @@ class PreparedBuild(object):
   def get_display_name(sha):
     return sha[0:7]
 
-  def tags_from_ref(self, ref, default_branch='master'):
+  def tags_from_ref(self, ref, default_branch=None):
     branch = ref.split('/')[-1]
     tags = {branch}