[Roassal2] RTResizable leaves callbacks with each selection

Hello again

This time I bring a problem without offering solution because I haven't managed to look deep enough into it yet.

RTResizable leaves callbacks for handles on the selected element even afrer deselection (calling RTResizable>>#removeHandles). It means that following screnario happens:
- I click on element
  -> handles are created and their callbacks are created
- I click anywhere else
  -> handles are removed but their callbacks are not removed
- I click on that element again
  -> handles are created again but new callbacks are created
...etc...
So with each select, new callbacks are created and are added to previous ones.

Those callbacks are created in RTResizable>>#showHandles - RTResizable>>#attachHandle:toCorner: - RTConstraint>>#stick.

I did not notice any performance (or other) issues caused by this in Roassal resizableExample, but it causes performance problem in few (but important) cases in our DynaCASE (I am not sure why only there).

Jan