WIP: Refactor study description

This WIP pull request is breaking up the study description handler in multiple UI modules, as well as breaking up the study handlers file to be hosted on multiple files for easy edition.

I still need to decompose the post of the study handler in multiple post-only handlers that will help to maintain the page.

Feel free to make any comment if you feel that there is something really wrong.
@antgonza @ElDeveloper, I think we want to modify the nginx config to pass on host. See [here](https://www.simplicidade.org/notes/archives/2011/02/nginx_proxy_host_header.html) and [here](https://twitter.com/dongwoo/status/511572072019922944). The issue is that I _think_ the XSRF stuff in tornado (which we should enable if it isn't already) could muck with nginx. The specific issue with this line is that without XSRF, I believe this line is a potential security issue as headers can be spoofed. However, I don't think the consequences are great