Actually unmount when toggled

This should help out #21.

React silently accepting a parameter of the wrong type turned out to be a bug:
https://github.com/facebook/react/issues/2079

Test Plan:
Added logging to `componentWillUnmount` and saw it work.
Merge pull request #24 from dmnd/unmount-bug

Actually unmount when toggled.
Merge branch 'master' into feature/add_summary_tooltips