Move to react-components

Summary:
I replaced `BlurInput`, `ButtonGroup`, `InfoTip`, and `Tooltip` with
their react-components equivalent. I didn't yet replace `TeX` because
I'm not sure about the `typeof Exercises === "undefined" ||
Exercises.useKatex` line.

This is not quite complete yet - I need feedback from reviewers on how I
should get the styles. I'm tempted to move react-components over to RCSS
so styles will always be packaged with components. The other alternative
is to add react-components as a subrepo.

Test Plan:
* make server
* open dev:9000
* find an example of each component to play with.

Reviewers: jack, kevin

Subscribers: alex

Differential Revision: http://phabricator.khanacademy.org/D9370