Make Dictionary tool use Gecko control

* Implement menus per LT-15412
   - Add tests for behavior to drive menus
   - Add support code to enable menu behavior
* Implement an XhtmlDocView that displays the dictionary
  in a Gecko web control
* Configure FLEx to use the new view in the dictionary tool

Change-Id: I42b205501a8720168ec97f01d0b059f3bf9f64f6