Add form plugin
Add form plugin

Adds new form plugin, which blurs() focus on impress:stepleave. This is to
prevent an input field from being focused when it is no longer visible.

Related to supporting forms, in an earlier commit we already changed the
navigation plugin to only listen to keypress events from body and html
elements. This was to allow presentations to have, for example, form
elements, where users can type text, including spaces, use arrows, etc.

impress/impress.js,impress/impress.js