Allow RichTextFields in the Admin

Here is the change for the issue brought up at the google group: https://groups.google.com/a/fusionbox.com/forum/#!topic/widgy/7t8TBTff3UM

I am not sure what @rockymeza is referring to: 
> (We need a way to remember to do this for all of our projects though.)

Does this create a problem for your existing accounts? 

I have a pull request at mezzanine for the other portion: https://github.com/stephenmcd/mezzanine/pull/1011