gui acquisition: more improvements on the gauge
gui/buttons: Fix label not updating after GenBitmapTextButton.SetLabel()

Should go into GenBitmapTextButton, but for now, we workaround it by putting the fix in
our own sub-class
gui acquisition: improve a bit the progress bar display
gui acquisition: fix cancelling of acquisition

also ensure that callback are called in main thread (otherwise, it would crash the GUI randomly)
gui acqmng: add timer update

automatically force a progress update of the future at regular intervals

this allows the GUI to be much smoother in the progress update
gui acquisition: don't listen to old pubsub events

without this fix, we would crash on the second acquisition dialog because the change settings events
would call the first (already destroyed) dialog
gui acquisition: clean up widget

remove unused label
+ add variable to viewport => we can connect it to the view