ButtonSettings: In-line headset button: CheckBoxes have 2 states. Let's act like they do.

Change-Id: I9bdcc868b36445d71674babb8a31d0bd413c1155
ButtonSettings: return before returning super's onPreferenceTreeClick's return value.

Change-Id: I3a2c55c0722ea243a88f6aec9c105b11b9fe18c8
ButtonSettings: Consolidate some redundant CheckboxPreference handling click code, and inline a method called from one place.

Change-Id: I1e0da859d5fed002064bb88dfb5539623b429ca3