Initial version of broadcast/onDemand id synthesis. Ids aren't hashed yet though.
Add new GenreMapping, as existing mapping interface was not flexible enough to accomodate BBC style genres.
Add NitroGenreMapping, and appropriate test cases.
Misc TVA improvements:
 - Refactor OnDemand generation to account for 1:many service mapping.
 - Pass through MasterBrand on content.