No longer cursor insertion in SessionController.startEditing, fix cursor removal where missing
Fix incomplete destroy of SessionController
Add gui.EventManager.destroy()
Fix InputMethodEditor.destroy not unsubscribing from all events
Merge pull request #387 from kossebau/fixStartEndEditing

Unbreak Editor loading a new document with same canvas, but new session & controllers
Clear the stylesheets in OdfCanvas inside refreshOdf