* Add podcast_appearances joined table (forem#82)
* Add podcast appearances keys unique constraint and creator property (forem#82)
* Add podcast_appearance role validation forem(#82)
* Add spec test for podcast_appearances model (forem#82)
* Small refactoring - place podcast appearance association by alphabetical order
* Adapt m2m association to pass rspec test (forem#82)
* Rename podcast appearance model to podcast episode appearance and remove fk indexing
* Rename podcast appearance model to podcast episode appearance and remove fk indexing
* Rename podcast episode appearance models and spec models. Update podcast episode and user spec tests (forem#82)
* Rename podcast episode appearances composite index to follow Rails naming pattern (forem#82)
* Remove ddl_transaction disabling and conurrent index adding from appearance migration
* Add role validation in model spec (forem#82)