Allow text selection in focused elements

This is for better interaction with contenteditable divs.
Fix scrollbar handle size calculation
Make sure move handle is always as tall as header
Bugfix for a previous bugfix in manual column move

If you clicked the move tab on a column while you were scrolled over to
the right, you'd get a bad move and a potentially illegal one. The
reason is that the colOffset was being added in to the endCol twice.
This only shows up when you click and *don't* move the column, because
when you *do* move the column, endCol gets computed again in a
different place, according to a correct formula.
Fix some things that could break undo
Honor isImmediatePropogationStopped in text editor
Fix some problems with copying/pasting rows

We were getting an extra line when we copied and pasted a row. Turned
out lots of things were conspiring to make this happen.
Fix bug: hit delete in cell, then can't type
Undo overzealous change to SheetClip

Turns out we do actually want to pop one line. Bug this caused: select
one cell, copy it, then paste it; you end up clearing the cell below it
(!)
Re-enable wrap-on-populate, except for paste

Turns out killing the wrapping was a little overzealous and broke
autofill.