Figure out SocketIO test client and add basic testing for transcription process

[reuben]

[reuben]

I've added tests in #11, so now rewording this issue to cover the missing part which for now is throwing exceptions deep in internal pytest/Flask/SocketIO code so I'm clearly getting something wrong in the testing setup. Once that's figured out we can test a simple "start", "emit-data" with PCM for a small file, then wait for "recognize" with correct results.