Add return item eligibility validator and associated state machine updat...

- Add a PORO to determine if an item should be returned, manually intervened, or rejected
- Add state changes to Return Item state machine that use this eligibility validator
- Add a column on return item to store any reason that the validator might return about its rejection/manual intervention status. This is going to be used in an admin panel currently being worked on by @richardnuno and @jordan-brough 
- Default rule: If it has been less than 365 days since the item has been purchased, it can be returned, otherwise reject. Allows for people to write their own customized rules pretty easily.