Redo of most of PR #530, without the cruft.
Manually applied changes from PR#3@jamalex.
Added cute images back in, for @bcipolli.
Updated topic tree data, with partner content excluded.
Merge commit '3fbf1886b5ffec93c45329c8628eeeff1f27bfa4' into HEAD

Conflicts:
	.gitignore
Khanload now deletes exercises due to missing file, not missing old entry.
Styling fixes on the exercise pages.
Tweaks to khanload command, added a few exercises to blacklist.
Updated topic data.
Merge pull request #531 from jamalex/update_topics

Update topics and remove partner content: Replacement for PR #530
Woot woot