Associate batches with HIT types.

The testing login part of this code is a bit messy; any suggestions?
Fix error reporting on login.
Merge branch 'master' into batch_per_hittype
Blaze fix for batch admin page.
Use the HIT's batch. Start removing the concept of an 'active' batch.

This will break the lobby for now.
Start fixing tests.
Expose batch on the client too.

Seems messy to duplicate this code.
Merge branch 'batch_per_hittype'

Conflicts:
	client/helpers.coffee
	client/ts_client.coffee
	lib/experiments.coffee
	tests/utils.coffee
clean up testing login after merge; fix broken tests