WUI: Bumped to GWT version 2.7.0

- Fixed loading logo in wui-admin.
- Removed unused dependency from pom.xml
- Removed Opera permutation since it's not supported by
  GWT 2.7.0

- Thanks to new version of GWT we can now run superDevMode
  from command line like: "mvn gwt:run". It will start both
  servers and new mode again recompiles on browser refresh.