systemui: fix moar memory leaks

used example commits in AOKP & CM to fix memory leaks within Vanir source using
onDetachedFromWindow to unregister content resolvers that were being left behind
every time the view was redrawn

PS2: searchpanelview: move setdrawables back to onfinishinflate
     change signalclusterview's updatesettings back to our feature
     style instead of aokp's

PS3: good to go

ps6: prevent double-observe and double-unobserve of SettingsObserver

Change-Id: I09c15bfe78ad5edab6a279d4695153313c9dfbdf