jquery.confirmable: New inline confirmation module

$().confirmable() can be applied to any inline-block element. It will
cause it to expand into "Are you sure? [Yes] [No]" question and
buttons when clicked, where the buttons are clones of the original
element: [Yes] will carry out the default action (or a different one,
if specified), [No] will collapse the interface back.

Possible uses include:
* Confirmable "rollback" links
* Confirmable "unwatch" links on watchlists
* Confirmable "thank" links (Echo extension's ones)

Added a demo with possible uses on history and watchlist pages.
Included Hebrew messages courtesy of Moriel.

Change-Id: I2f6e0bd4f6f0a84e1a0d7193cde076738f3cdd25