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.

Test if thesis is vetted/deleted and mail is sent in
the accepted/refused case.

Theses that are accepted are vetted by the correct contributor.
Mails are not yet sent. Thesis is not yet deleted when refused.

Work in progress. All unvetted theses are now listed at
theses/unvetted_thesislinks. Vetting editors click on
a thesis link to vet, and are redirected to
theses/vet_thesislink/<id>, where they can change fields of a thesis
link.

theses/vet_thesislink/<id> is now a regular update view. It does not have
mail capacity, or refusal reasons, etc. I will work on that next.

I keep get weird bugs. Maybe merging in development will help.

Markup logic should be in templates, not in model layer.

Partial template is named _header_as_table to signal
that it is ment to be included into other templates
(analogous to the private method naming convention.)
The full text of several of the thesis link's fields
(domain, subject_area, etc.) are fetched from constant dicts
in custom filters defined in theses.templatetags.theses_extras.

This does not work yet. I wrote some failing tests, but while
I was doing that, I came to the conclusion that I want to make
the route of the get request different from the route of the post
request.

Move few constants to a seperate file away from models.
This implies minor edits in other apps relying on
these few constants.