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.
Thanks, currently it is used only here, but I can see that we might want to perform these checks in other points.
Just a note, this can be even more simplified:

```python
def _approve(level):
    return True if not qiita_config.require_approval else level == 'admin'
```