Add Cam's extra buttons.

Summary:
1. This adds basic relations: =, <, >
2. And advanced relations: <>, <=, >=, ~
3. And the option to show a \div button in the basic button set.

Reviewers: alex

Reviewed By: alex

Subscribers: cameron, aria

Differential Revision: http://phabricator.khanacademy.org/D13786