Fix for filling TinyMCE widgets

The current method of filling TinyMCE widgets (by calling `send_keys` on the body element of the iframe) is not working for me.  The `send_keys` call seems to do nothing (and so the tests which expect it to do something fail.)  I'm using selenium 2.24.0, Firefox 24.0.

This implements an alternate means of filling the TinyMCE widgets.  I think this should be generally more robust.  I am no selenium guru, however.  Perhaps there is a better way.