User pages

https://github.com/pfraze/phoenix/issues/155

![gifrecord_2014-11-10_135709](https://cloud.githubusercontent.com/assets/1270099/4982600/fe684e38-6913-11e4-84dc-7bf58963558b.gif)

In this gif, demo.js is a user page. Right now, phoenix finds all `.js` files in `./user` and auto-adds them to the sidebar. They are browserified, then rendered in a page with the bootstrap styles inlined. They are not allowed to make outbound requests, but they do have access to an RPC api.

Look at `./user/demo.js` in this branch to see an example user page. Look at `./web_frontend/src/lib/sandbox.js` to see the api it has available.