Get rid of all non-english language files.

Summary:
This makes ckeditor only usable in English, but removs 680 files from
third_party.zip, which should help webapp startup time.  (The problem
is that any import from third-party has to read third_party.zip, so
the smaller third_party.zip is, the faster that read happens, since
appengine is bobbins for reading files.)

This is pretty much a hack, and I'd like to find a way to get these
files back.  We should feel free to roll back this change if we ever
need these files for anything, and figure out another way to save
start-up time.

Test Plan: Fingers crossed.

Reviewers: tom

Reviewed By: tom

CC: ben

Differential Revision: http://phabricator.khanacademy.org/D4623
Add some newly-enabled plugins to the CKEditor build process.