Make the preview use real generated XHTML and css

* Modify the DictionaryConfigurationController to know about
  the current item and mediator for the style sheet.
* Dump css to file for the preview
* Export string for XHTML with a link to the css file
  and load it into the gecko control.
* Also tried to tweak the gecko control size to fit the dialog
  better.
The css does not appear to be applied by the gecko control, possibly
a problem with the gecko control its self.

Change-Id: I7587dd512b39e1888884cd4208cfa8cb92abbbff