Updated get_data and get_course for PG support.
 - get_data wraps get_data_for_level, so prevent
   breaking API changes.
 - Updated API model to support levels in course
   retrieval and caching methods.
 - Rationalised routing accordingly.
Use iid vs id
Merge branch 'refactor/datasplit-ug-pg-api' of github.com:unikent/programmes-plant into refactor/datasplit-ug-pg

Conflicts:
	application/models/api.php
Merging changes
Start fixing tests
Tests pass once more