This commit contains the removal of html from 'the important' models
 or at least contains replacements for model methods such as `print_as...()`,
 etc. etc. Except for `header_as_li`, methods are not completely deleted yet.

> Fixed/Improved the nested comments and comments in reports. They were
 not shown before.

> Improved DRY principle in several templates/codes.

> Created Managers in the `submissions` app to filter i.e. "pool" submissions
 (so exclude potential author from judging on his own publication) for the
 pool view in the query; not in the template!

> More...

Fix bug that allows a forged post request to create a comment,
while the submission is not open for commenting.

Only works for comments on thesis links. All comment forms
should post to this link from now on! (So all logic pertaining
comment creation should disappear from the models' detail view.)

I also added a `new_comment.html` partial template and added tests.

I had replaced ThesisLink#header_as_li with a partial template,
but forgot to replace it in some places.

The 'As contributor' author field contained raw variables that were not
within tags.

The datepicker behaved weird in firefox, and I think fixing it
has no priority now. I've created the VettedThesisLinkFactory
and wrote a couple of happy-path tests for the theses view.

Also fix missing template error for modified thesis links.

The Comment model now has a option to
 append a file (pdf, png, jpg) to itself.

Change all involved tests. Start moving email to templates.

Update all involved tests. Also extend model_form_data to
accept an argument `form_kwargs` to pass to form.

Creating a new ThesisLink didn't save the `requested_by`
 field, causing trouble in for example the vet view
 for these specific objects.

Improve the templates using template tags.
 Further, wrapping the `content` block in the
 `container` div element.