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.
Still amazed that Python doesn't have a switch/case. A different pattern that can be used here which requires only a single comparison is:

```
actions = defaultdict(
    lambda: self.unspecified_action,   # would need to define
    process_sample_template=self.process_sample_template,
    create_raw_data=self.create_raw_data,
)

action_f = actions.get(action)
msg, msg_level, top_tab, sub_tab, prep_tab = yield Task(action_f, study, user)
```