Added tests for SparksController, including failing tests for behavior when creating a spark that already exists.
Added handling for creation of already created sparks, with new user being added to the spark.
Changed HTTP return code for adding a user to a sparkto be 200 OK, rather than the innappropriate 202 Accepted.
Removed update action from Sparks controller.
Added tests for sparks controller destroy method.
Implemented SparksController#destroy method, fixed errors in tests thereof.
Merge pull request #33 from maxluzuriaga/master

Functionality for creation of duplicate sparks & ability to destroy user associations to sparks