#6 Add custom block support to the API and update to latest GC version

Added a CustomBlock class that can be inherited and a CustomBlock attribute that should be added to it that describes the properties of the block. The block gets an ID starting from 500 at the moment, I intend to use the persistence API to store the mapping between block IDs and the block type's full name so conflicts don't happen or are resolved automatically. There's a test block in the test class but for that test block to be tested it needs the extra assets I used for testing (but it should deal with that not being set up). Breaking changes coming from FMOD 2.0: - Audio[int index] changed to Audio[PARAMETER_ID index] - Audio.Parameters removed