[pencil] Send messages to live-edit iframes.

Prototype of a hiding toolbar, tested in Google Chrome canary on
Windows XPP and Chrome Beta under Android 4.2.2.
Leave small gap to left of toolbar, fix path quoting in pencil.html

Force 4em gap on the left of toolbar for first line of file or first
entry in filelist to be visible.
Double-quote Scout.socket path argument so that file names including
single-quotes become useable (currently causes file to be inaccessible
after creation).
Merge commit 'cc28c1e' into scroll_download