Drag left/right on backspace to mark+cut

[lineinthesand]

In some apps/keyboards, when you drag left on the backspace button, the content to the left of the cursor is highlighted progressively, one word-boundary at a time, and when you release, the highlighted content is cut, ready to be pasted elsewhere. Likewise, while dragging to the right, after having dragged to the left, the highlighted selection is reduced again (if you've highlighted to much upon dragging left).

This behavior is different from the swipe-left action proposed in #156 but a similar end could be accomplished with my proposal, provided you drag far enough.