Disable annotation mode on read-only projects

Closes #1246 (closed)

I hid the Annotate button on read-only corpora or corpora that are not loaded yet, and added a watcher on the annotation panel so it decides to die when we know that we do not have a write right.

This watcher allows us to not have to bother checking the rights in other components such as the InteractiveImage, which may not even have access to the corpus ; the enabled state in the annotation store will never be true when the user doesn't have a valid right. If the user somehow manages to activate the annotation mode without the Annotate button, the annotation panel will kill that anyway.