Put generated thrift code in its own module

It would be nice to also control the compiler warnings a bit in the thrift-generated code. It would make it less spammy. If in its own module, the compiler flags could be overridden to ignore the warnings. If it stays in with the rest of the code, then some `@SuppressWarnings` annotations should be added to the classes immediately after generation.

It's probably a good idea to isolate the generated thrift code from the rest of the code base, anyway, so putting it in its own module might be easier.