- The 'save' button is disabled and shows 'No changes' at first. Editing contentEdit's text
enables the button and makes it show 'Save'.
- The 'save' button is disabled and shows 'Saving...' when the page is being saved, and stays
disabled until contentEdit's text has been changed again.
- The 'save' button shows 'Saved' once the page has been successfully saved. fixes#560
- contentEdit is readonly when the page is being saved