Add global shortcut to begin listening

[Equinoxx4978]

Feature summary Add global hotkey to trigger song recognition. Implement through Freedesktop GlobalShortcut protocol.

How would you like it to work In app preferences allow the user to add a hotkey to "Trigger Listening". When hotkey is pressed Mousai starts listening, then once the result is found the UI opens to the result.

Relevant links, screenshots, screencasts, etc. None.