When several bufferviews exist for the same inset, the data that depends on the view width have to be BufferView-dependent. While this is the case for several mutable members of InsetCollapsable, some were missing.
This commit makes button_dim_ (renamed from button_dim) and openinlined_ bv-dependent.
Get rid of the hitButton function.
Remove the bv-independent geometry() method and implement editable() explicitely instead.