Strip types

The JSXTransformer (since v. 0.12.1) supports a flag for stripping [Flow](http://flowtype.org) type annotations.

This PR allows the `stripTypes` flag to be set next to the `harmony` flag in the require.js config, and it will be parsed along correctly.

This flag is not supported by JSXTransformer v. 0.12.0 (the currently bundled version), but since this project works fine with the newer version, I still think that this feature makes sense.
Now that we have another option, I would prefer getting rid of the ternary operator. The code below can accommodate more options more elegantly.

```js
var transformOptions = {};
if (config.jsx) {
  transformOptions.harmony = !!config.jsx.harmony;
  transformOptions.stripTypes = !!config.jsx.stripTypes;
}
```