Remove notification level after hiding. Fixes #200

    Not sure if hide() could ever be triggered without triggering show() first,
    but set the level default inside hide() just in case.
Fixed an issue with annotationsLoaded event
Fixed an issue with annotationsLoaded event
Make notification tests fail right
Merge branch 'issue_200_notifications_cleanup' of https://github.com/6a68/annotator into v1.2.x-new

Backport from master.

Fixes #200
Closes #270
Fix bad enum value on Annotator.Notification