Revert "quicksettingsmodel: use generic a settingsobserver"

The brightness needs to be separate (at least). It changes a lot more often than the other 2.

This reverts commit 309804f03f65abe8f32ecc60df9286d415c1b3b1.

Change-Id: Ic21640a03380d6494509972b47d2e78046e3d330
Merge "Revert "quicksettingsmodel: use generic a settingsobserver"" into kk44