Space Barnacle Incursion

More work here than I anticipated. Spent a lot of time deciding what kind of system to model, and then on the types of associations.   Had trouble deciding what kind of custom methods I could implement. Unsure how to test more complex validations like inclusions.  Also wanted to implement a "one captain per ship" validation but wasn't sure I could refer to parameters being given on creation within a validation.  Didn't get through all the seed data either.