Additional hints for remainders

Summary:
Change exercises to meet standards

Move remainder code into Divider object

Get divider working for non-decimals

Make division test exercise

Fix Divider for decimals

Decimal tests

Get division working with decimal remainders

More tests

Update exercises to work with new Division object

Further tweaks

Test Plan: Make sure all the exercises in division_tests.html look good. Also try the exercises in division_x.html, dividing_decimals_x.html and converting_fractions_to_decimals.html.

Reviewers: eater

Reviewed By: eater

Differential Revision: http://phabricator.khanacademy.org/D9094