Add JSON serialization/deserialization using Gson.

Not a huge fan of the way this is looking.
Add CAN message data back to comparison.
Remove log output when running a few tests.
Hack up a way to pull ArrayList payloads from deserialized JSON.
Leave floating point frequency out of DiagRequest comparison for now.
Merge branch 'refactored-datastructures-checkpoint' into refactored-datastructures