Use input values between 0 and 1 for osdWindow
Using floats or doubles instead of integers allows for more precise values of the slider. In particular this fixes a bug where the cast to int was done inside gnome-settings-daemon and near-0 values would get casted to 0. As a result, the volume icon (silent) and the slider value (0) don't match anymore.
Since we're using values between 0 and 1 inside barLevel anyway, this allows removing levelBar, too.
Depends on: gnome-settings-daemon!78 (merged)