[added] Router.renderRoutesToString

[fixed] Initial render to null causing second render
[fixed] Query not passed to willTransitionTo
[fixed] ActiveState mixin causing second render
[added] Transition to throw http status 302 on redirect
[added] setTitle helper to change document.title can be used as helper
or prop (title) on route
[added] NotFound route component
[added] Docs

```js
Router.renderRoutesToString(routes, originalUrl).then(function (data) {
data.html; //string returned from React.renderComponentToString
data.httpStatus; //number to be used as the httpStatus, <NotFound />
routes will cause this to be 404
data.title; //document title from setTitle helper
}).catch(function (error){
//Redirect will set error.status and error.location
error.status; //302 for Redirect
error.location; //location to redirect to
});
```
Merge branch 'server-render'