Add handlers for lowering/restoring pulseaudio vol
Add handlers for lowering/restoring pulseaudio vol

====  Tech Notes ====
pulse_lower_volume() scans through the list of running input sinks and
reduces the volume to 30% of original volume skipping over the stream
named 'mycroft-voice'

pulse_restore_volume() restores the volume again.

If activated with the 'pulseaudio' config parameter they will be called
when mycroft starts/stops listening and starts/stops speaking

==== Environment Notes ====
The Audio->pulseaudio configuration parameter can now be set to 'lower'
to activate this feature

Dark5ide/mycroft-core,forslund/mycroft-core,Dark5ide/mycroft-core,forslund/mycroft-core,linuxipho/mycroft-core,MycroftAI/mycroft-core,aatchison/mycroft-core,linuxipho/mycroft-core,aatchison/mycroft-core,MycroftAI/mycroft-core