react-with-addons build

This creates a new standalone build which should have everything the
default build has, plus a little extra. This is not a sustainable long
term solution (we shouldn't make people choose like this) but it fixes
the problem we have in the short term.

This also removes the terrible react-transitions build. This is better
anway.

Fixes #369

```
Running "compare_size:files" (compare_size) task
   raw     gz Sizes
320704  62665 build/JSXTransformer.js
462810  96559 build/react-with-addons.js
 96721  27035 build/react-with-addons.min.js
429162  89475 build/react.js
 90003  25164 build/react.min.js
```

Let's hold off merging until:
- [x] We're happy with what's on `React.addons` (as the repo stands today)
- [x] We update the release tasks so `react-with-addons.js` gets added to the bower repo & starter kit
- [x] Addons builds end up in `react-source` gem
- [x] Addons builds end up on builds server
- [x] We have example(s) using this build
- [x] Update docs to mention the new build and the things that go along with it. - #314