Rightmost selection is lost and seqpanel not repainted when selecting columns offscreen by dragging left

The rightmost columns at beginning of a click-drag left on the alignment ruler are deselected when mouse re-enters window after dragging left to select columns to left of visible region. The sequence panel is also not being repainted to reflect scroll to left (also check scroll right here).

Followon from JAL-3075,JAL-3074,JAL-3073,JAL-3072 - revise implementation to ensure:
1. SeqPanel repaints occur as scroll-left happens.
2. Selected range is not reset to left-most-visible-column when mouse is brought back into the alignment panel frame.