Revert "Revert "quicksettingsmodel: use generic a settingsobserver""

This only updates the brightness (auto/manual) value when the user changes it.. not
as the brightness level changes. doing 2 extra getInts after a user change is better than
allocating resources for two additional inner observer classes that are active all the time
in the quicksettings' handler

Also, the refreshview calls in the on______changed() methods also only work if the views are
attached to the window which doesn't happen because the brightness dialog collapses the panels

Change-Id: I673a8d24ee116916fb75b79de27471acad8b145c
Merge "Revert "Revert "quicksettingsmodel: use generic a settingsobserver""" into kk44