pyee 8.1.0 adds a small change to make the once call to be more safe in
multithreaded environments.
This switches back from the now deprecated BaseEventEmitter to the
standard EventEmitter.
Some dependencies aren't actually required but can be optionally
installed for extra functionality.
The Chromecast is an optional audio backend
VLC is an optional audio backend
pyalsaaudio is only used by the mark1 enclosure
google-api-python-client is an optional STT backend, by default Mycroft
uses the Mycroft servers