Use Redactor in iframe mode

I've been attempting to use the richeditor (Redactor) on a few fields in my plugin and have realized that Redactor seems to be hard coded to be in 'fullpage' mode.

Docs for this mode can be seen [here](http://imperavi.com/redactor/docs/settings/#set-fullpage)

In this mode it creates markup for an entire page (includes ``<html></html>`` tags) rather than just the markup for a content block. I wasn't able to find anywhere in October utilizing Redactor in this way, so I'm not sure why this mode is implemented.

Maybe a better solution is to be able to change how Redactor is initialized, but this commit makes the richeditor field type useable for simple content block editing.