Fix event listeners not being removed on _exit
Fix event listeners not being removed on _exit

Fixes the geoOn/geoOff to stop using anonymous functions so removing a
widget will actually remove the event listeners.

OpenGeoscience/geojs,OpenGeoscience/geojs,Kitware/geojs,Kitware/geojs,OpenGeoscience/geojs,Kitware/geojs