Add school grade as an option

Problem/Motivation

Add a grade level rating as an option to show along side the regular rating. This should be configurable, globally, as there are different grading systems around the world.

User interface changes

- UI for admin area to change global settings
- Add the ability to turn on/off the grade level to settings form per field
- Add grade level to rating area

API changes

None.

Data model changes

Config additions