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

It's 2 extra getInts whenever the brightness changes... so this commit would significantly lag the statusbar brightness slider.

This reverts commit a5418ac077b7c454d0c09e52fb746ab163aa02eb.

Change-Id: I187b9ea0c18e3922fa8e4bdcaafd5e8b1cdd714f
Merge "Revert "Revert "Revert "quicksettingsmodel: use generic a settingsobserver"""" into kk44