This avoids opencoding it in lot of places (See #20)

This allows other objects to interface with the layer shell API.

This is currently the display size excluding the static panel

so we can easily emit the changes signal

since they're reserved.

Thanks: Bob Ham

Make phosh struct a PhoshShell gobject so we can emit signals.

Reviewed-by: Bob Ham <bob.ham@puri.sm>

so we can add further background handling there

Reviewed-by: Bob Ham <bob.ham@puri.sm>

will be tied to iio-sensor-proxy in the future

This adds a common base class PhoshMenu for all top panel menus so
phosh.c itself doesn't need to care about the details and we don't
duplicate the code.