Annotator.showEditor now saves changes

before that change, showEditor would just show the editor without saving
the annotation when the user hits save. All the logic was in
onAdderClick.

Plugins like https://github.com/aron/annotator.touch.js did not save
annotations, because showEditor did not save it. The plug-in could 
re-implement the logic in onAdderClick but I would consider this 
implementation details that should be handled inside the annotator.