New aliases for YouView schedules

- Allow override aliases to override the values provided
  in the channels feed from PA
- Add support for Scotland radio services using the
  prefix http://scotlandradio.youview.com/service/
Add YouViewCoreModule

Splits out lookup functionality, which is required by
other modules, from the ingest functionality. This means
that ingest can be disabled without affecting other
modules dependent on youview data, e.g. equivalence.
Include context in exception message
Add publisher mapping for new publishers
Changes from code review
Merge pull request #593 from atlasapi/youview-service-overrides

New aliases for YouView schedules