Add grouping of tree nodes by shared ancestry to Aptx

The current Jalview tree viewer allows users to divide the tree in groups according to common ancestry by left clicking in the tree view. The x position of the mouse click determines the cutoff for shared ancestry, sequences that share an ancestral node that is to the right of this x coordinate are then grouped together.

This functionality should be ported to Archaeopteryx, the grouping will also need to be reflected back onto the original alignment.