Add support for MozillaTTS engine

[flightmansam]

This is a working PR so far it is a minimum viable product and lacks preferences.

How to run, install mozilla-tts with python as in these instructions (pip install TTS). Run the tts server (with default port, 5002), tts-server. There will be a small pause as the first query returns, but then should run smoothly

TODO:

• [ ] Fix up sentence chunking.
• [ ] Ignore or merge singlew word requests (mozilla-tss kinda mangles this request)
• [ ] Fix preferences page
• [ ] Fix play pause and all those extra goodies
• [ ] any type of error handling on the tts api side

[ImperialSquid]

Small fyi, ZoTTS can now do engine status error reporting if part of the initialisation goes wrong.

Check out the status reporting function for how it works (essentially, you should save a value to the optional errorMsg field, refer to WSA's init function for an example).

The messages you want to send should be registered in the localisation files, (the syntax is available here), if the engine has standard keys, using those would be good, but you can also add custom ones if you need to.