0.7.3: Dock the bar on a frame edge like the navbar; fix the dead drop

The drag never rebuilt anything: the touch listener cleared the
dragging flag before calling dropBar, so the drop returned at once
and left the ghost handle up and the bar invisible. The bar now
docks like the navbar instead of floating: a release redocks it
flush with the frame edge nearest the drop, edge and along-edge
position persisted, chevron pointing in from that edge.