add alert for autosaved version on edit

Ticket

+commit
 

People don't discover autosave, and people who know it's there edit again and lose their autosave before realizing it.

 

If there is an autosaved version, then when you edit, an alert message appears just under the card header (like requests about memorizing passwords in your web browser), letting you know there is an autosaved version, with a link to it (in the Changes tab).