Split podcast DAO into a simple dao & caching decorator

This was the original intention.
Remove all references to EpisodeDAOImpl.i()
Remove duplicate db methods from assistant classes
Split episode DAO into simple & caching classes
Reformatting and TODOs in SimplePodcastDAO
Ensure tests start with a clean DB
Fix a local delete testcase

Locally deleted podcasts do not return the same Podcast object instance.
In fact, I'd like to redo the entire local actions concept.