Implements a rough outline of the SNI (StatusNotifierItem) d-bus
protocol for tray icons.
Note: This is currently *very* WIP
Full implementation will close https://github.com/scorpion-26/gBar/issues/5
Due to the fact, that we needed to manually propagate hover events from
the slider, two hover events are sent when coming from the side of the
slider. This we need to await BOTH close events until we can call the
leave function.
There seems to be a floating point error somewhere though, since
sometimes it goes up by AudioScrollSpeed - 1 instead of
AudioScrollSpeed...
For the ping https://github.com/scorpion-26/gBar/issues/5
gLib will not immediately run the callback after the timeout has been
added.
This caused everything to be a few ms late.
Now the timeout will trigger early by default.
