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.
_might_ be doable with a `groupby` too:

```python
files = {group: list(grouped) for group, grouped in groupby(files_tuples, itemgetter(fpt))}
```

But that assumes `file_tuples` is sorted. If it isn't, then:

```python
files = {group: list(grouped) for group, grouped in groupby(sorted(files_tuples, key=itemgetter(-1)), itemgetter(-1))}
```

Though that is arguably more complex to look at...