SB2: remove {Begin,End}ModelFill() in UnhideListViewBase.
Util: moved QML unhide stuff from SB2.

Moved UnhideList{Model,ViewBase} to Util since a bunch of different
plugins may want to use it.
Util: UnhideListViewBase API improvements.

Added SetItems() method and itemUnhideRequested() signal, now the class
is basically usable without subclassing on its own.
HotSensors: initial work on adding sensors back.
SB2: abstract from ViewManager in AutoResizeMixin.
Util: moved AutoResizeMixin from SB2 here.
HotSensors: proper unhide list positioning.