Extensive changes to channels and channelGroups to support xml.
1. ChannelController and ChannelGroupsController now implement BaseController
2. ChannelSimplifier has been migrated to use the AtlasModelWriter, and refactored extensively
Moved the channel numbering simplification test to reflect the move of the simplification code. Also a bug fix in the simplification code.
Merge branch 'master' into mbst-4019-ingest-pa-channel-data

Conflicts:
	src/main/java/org/atlasapi/query/v2/ChannelSimplifier.java
	src/test/java/org/atlasapi/output/simple/ChannelNumberingSimplificationTest.java
Merge pull request #226 from atlasapi/mbst-4019-ingest-pa-channel-data

Support for XML on the channels/channelGroups endpoints