Clicking inside a selected region in the Alignment Editor should reset the selection to the clicked character

Sequence Area in the Alignment Editor should behave the same as Name List area: if multiple sequences or columns are selected and a user clicks inside the selected region a the selection should be changed to a 1 cell.

Scenario:

1. Open "COI.aln".
2. Select a region in the Sequence Area.
3. Click into the middle of the region.
   Expected result: only the clicked cell is selected.
   Actual result: the selection is the same.