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...

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.

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

A blank domain throws an error in /theses/.
I've also installed factory_boy (pip install -r requirements.txt
to get it) and set up a ThesisLinkFactory and a unit tests that
tests whether ThesisLink validates for a blank domain field.

Not sure if this is exactly how you're supposed to validate
a model, but it's a start. First unit test of the project, whoohoo!

This is recommended. Also give names like
MASTER_THESIS = 'MA' to avoid magic strings and allow for easy
reference, e.g. thesis.type = ThesisLink.MASTER_THESIS. This sort
of thing helps in maintainability of the codebase, since if we want
to change the abbreviation to 'MASTER' for some reason, we have it
defined in one place, and not in 100 places in the code.

I've opted for hanging indentation

foo = long_function_name(
    var_one, var_two,
    var_three, var_four)

instead of aligning with opening delimiter

foo = long_function_name(var_one, var_two,
                         var_three, var_four)

because the former makes more sense to me. See
https://www.python.org/dev/peps/pep-0008/#indentation