Upgrade to react 0.13 and dependencies

[toolness]

This fixes #294 and upgrades us to React 0.13, as well as the latest versions of react-bootstrap, react-ga, react-router, and react-select.

In general this consisted of the following changes:

• Getting rid of the HTML prettification of React's generated HTML. React now notices that there are more text nodes than before and issues a warning, which disabling prettification eliminates. This is a bummer for view-source but will make our HTML files smaller and folks can view the prettified version with goggles/devtools anyways.
• Ensuring that getChildContext always returns the exact same properties in tests to avoid spurious Parent vs. Owner Context warnings.
• Upgrading to react-router's new use of this.context.router instead of the Router.State and Router.Navigation mixins. This entailed creating a new StubRouter class for our tests.

In general, having the really good test coverage of our front-end codebase really helped here, as it surfaced problems very quickly.

[toolness]

Note that this PR will likely collide with #626. We should probably land #626 first, since it's more urgent, which means this PR is blocking on id.webmaker.org's stability.

[toolness]

Hey @k88hudson, curious what you think of this, since a lot of this code is testing code, and you're familiar w/ both react and react-router.

[toolness]

Ok, I think this is ready for review. @ScottDowne can you take a look?

[toolness]

By the way, whoever reviews this (and also, once it is merged) may need to manually npm remove react-a11y before running npm install. We stopped using react-a11y a while ago but it was still in our package.json, and because it has a peer dependency that requires React 0.12, an error may be raised, which manually uninstalling react-a11y fixes.

[ScottDowne]

Not sure if this is due to needing a rebase, or because of the upgrade.

The login logo is super large and it's not on staging.

The footer is missing some left padding or margin:

[ScottDowne]

It worked otherwise, just visual quirks.

[toolness]

Hmm, the footer issue you're seeing seems like a regression of #622, which was fixed by #646... but I'm not seeing that or the big Webmaker logo on my end. Can you re-try with my latest merge? If you're still experiencing those problems, what browser+version are you using?

[ScottDowne]

That seems to have done the trick, looks good now.

R+