added some stuff to enable bookmarklets w/ CORS support to exist.
minor copy changes for custom images.
Added some support for importing/exporting images via filepicker.io.

Right now it's disabled by default, and enabled if
window.FILEPICKER_API_KEY or localStorage.FILEPICKER_API_KEY is
non-empty.

Also turned off form autocomplete on the main form, since the dynamic
addition of new input elements was really confusing Firefox. Besides,
the form state is always in the querystring anyways.