Fix #1424636 - Fix undo issues with selections.
Fix #1424636 - Fix undo issues with selections.

- We just need to unhide the tool layer (which is updated by the
updateHandler() call), instead of calling ReDraw (which rebuilds the
selection and requires a subsequent call to
SelectionModeHandler.PerformSelectionMode)

- The selection's origin needs to be updated when the mouse up event is
received. This led to undo issues for selections that were adjusted with
one of the handles on the left.

jakeclawson/Pinta,Mailaender/Pinta,jakeclawson/Pinta,Mailaender/Pinta,PintaProject/Pinta,PintaProject/Pinta,Fenex/Pinta,PintaProject/Pinta,Fenex/Pinta