Add modes for hide volume extrabar

Some users do not like the fact that the volume extra progress bar is permanently displayed.
This PR fixes this.
To activate you need to add the field "hideextravolume" in LCD.xml.
This field can have the following parameters:
 - nav - hide in navigation mode
 - play - hide in playing mode

Options can be combined.
For example:
``<hideextravolume>nav,play</hideextravolume>``