AutoSaveable mixin.
Set assessment as published when submitting.
Autosave assessments and load unpublished.

Assessment records are initially created as unpublished and autosave 2s
after a change. When going to the new assessment route, it first checks
if there is an existing unpublished assessment and if so, uses that
instead of creating a new blank record.
Display some feedback about autosave activity.
Handle published vs unpublished assessments.
Merge pull request #48 from cyrusinnovation/autosave

Autosave assessments. Closes #34.