Start grade scale features. Added models and admin.
Add form, baseformset, and formset for grade scale

Also docs update to core/models.py
Add update view for grade scale.

And corresponding urlconf, template, styles
Style bugfix - label min-width

Tabular fields for wide screens will return once I figure out how to best display errors.
Bugfix - ModelForm Meta classes

Meta class attributes were being improperly used as class-level attributes. Not sure why it worked previously.
Change header name
Sessions added, grade scale removed

Semesters now tied to session with a DB backend.