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...

The modal is replaced by a customized text block
 which does allow for hover and click action by
 the visitor to filter by specialization.

Renamed the EditorialCollegeFellow to Fellowship.
 Now shows specialization code on the about page and
 improved the queryset from 2*#(fellowships) calls to
 two db calls total.

Front page will now show the last four publications of
 the current issue of SciPost Physics. Also reconstructed
 the .panels to .cards.

The .panel class should not be used again. This however can be
 replaced by the .highlight for headers or the -to be finished-
 .card construction. See Bootstrap4 docs.