Functionality for Ideas Controller, many more tests

Ideas controller now makes sure the API call passes in a valid lists of sparks before creating a new idea. Also made the "delete" functionality mirror that of a Spark (instead of deleting the idea, it simply destroys the relationship between the user making the call and the idea.)

Added tests for these new features and the rest of IdeasController's functionality.

Also added tests for the Idea model. (Up to 111 test cases now!)