Play song in playlist when tapped with a touchscreen

Double-click isn't a thing on touch; people expect things to react on a
single tap. Let's honor that assumption by making playlist items play
when tapped once with a tochscreen. To make the extra actions for
unselected songs more accessible, now playlist items' overflow menu
buttons are always visible.

BUG: 454343
CCBUG: 434437
FIXED-IN: 22.08