Fix #757: Selection: Listen for both touch and mouse/keyboard events

This revises event listener initialization logic to hook up both touch
and mouse/keyboard event listeners on webkit touch devices.  A flag is
set when a touch event is triggered, to avoid re-triggering Selection
events on emulated mouse events.
ColumnSet: Remove has("touch") conditions for touch+mouse devices
List: Default useTouchScroll false on platforms w/ visible scrollbars

This disables the TouchScroll module's behavior on platforms where
has("touch") reports true, but discrete scrollbars are rendered.

This is an admittedly somewhat loose heuristic, but achieves in
preventing TouchScroll from hindering on platforms that typically
have mouse input available, such as IE and Chrome on hybrid Windows 8
laptop/tablet devices.  These platforms generally do just fine with
native touch scrolling support, as well.

Unfortunately, there is no known foolproof solution to feature-detect
the presence or absence of a mouse.
DnD and util/touch: Tolerate mouse events on touch-supported devices
CHANGES.md: Note fixes for mouse+touch devices
Minor functional test code cleanup