Added active record associations and updated corresponding migrations
Added contoller files and added validations to models. Ammended timeslots migration.
* Added RSpec and tests for Boat and Timeslot controllers
* Modified controller to render JSON
* Modified migrations to correct earlier mistakes and set default values for initially null fields
* Formatted time from unix timestamp to postgresql friendly format
* Added database side validations in migrations
* Added cucumber
* Added controller logic for Assignments and Bookings
* Added many model validations
* Corrected migrations again
* Added as_json helper to Timeslot controller
* Added cucumber integrations tests
* Corrected Timeslots controller logic
* Finetuned validations and removed created and updated at fields from Timeslot JSON