Fixed unit tests
Removed the majority of the ?? errors for revisions

- The only remaining one is if the build fails to clone the repo (due to a bad hg clone or server shutdown)
Added try + catch to json loading so that we don't get a tracelog when connections are closed part way through
Fixed naming of column
Attempting to fix a crash where we have a None value as the revision
Replaced ?? with None values to be more clear
Merge branch 'front-end' into staging

Conflicts:
	master/buildbot/status/web/base.py
Merge branch 'katana' into autobahn_v1

Conflicts:
	master/buildbot/status/web/status_json.py