Technically speaking this is the largest change in my 2022 songticker sprint. This change moves the current nowplaying main loop into it's own thread and spins up an additional (threaded) api server. The api server receives http requests and sends them on to the main loop via an event queue.

• test most new functionality
• test input observers
• replace cherrypy framework bits with werkzeug
• add moar docs
• nonklangbeckeninput handling (is it's own issue: [input] nowplaying data for studio sources #173)
• assert queue being used in tests/test_api.py
• make --input-file (and reading it) optional/deactivatable

Fixes #38