i18nize 9 more major exercises

Summary:
Internationalize 9 of the easier-to-fix major exercises. Most of the changes
involved reverting sentence building, or cases where there were lots of strings
to mark up.

Test Plan:
Visit each of the exercises in local mode. Take all of the hints, make sure
there are no javascript errors, and make sure that grammar still makes sense.
Also, rebuild on webapp with `make i18n`, visit the exercises in box language,
and make sure there are no more english strings.

Reviewers: john, csilvers

Reviewed By: csilvers

CC: eater, alpert

Maniphest Tasks: T1036

Differential Revision: http://phabricator.khanacademy.org/D2599