Write tests and refactor html.

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.

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.

Edit styles to make old comment form better readable.
 This commit includes a new template which should eventualy act
 as a replacement for crispyforms which do not allow for
 easy bootstrap implementation.

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

CAUTION! READ ME!
This migration will setup a proper attachment environment.
This means, that for existing files (journal publication!),
 these folders/files should be completely moved to the MEDIA_ROOT
 folder, else this will return a 404 NotFound for the related
 files.

Improve comments app to follow PEP rules
 and remove all wildcard imports!!

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

- Alter field in_agreement on comment
- Alter field in_disagreement on comment
- Alter field in_notsure on comment
- Alter field is_cor on comment