Prevent autosave when no change was made to annotation

Steps to reproduce

• Select an annotation that was already created in document, either directly or through the "target" button in the Annotations browser
• Unselect (click in document outside the annotation area) without making any change to it

Expected behaviour

• No change should happen

Actual behaviour

• The autosave animation is triggered.
• The time for last change is updated to "a few seconds ago"