`Published` and `resubmitted` submissions dissapeared in the public
search results. They're back in the results as they were too strictly
filtered.

First working, not-tested, version of a multi-journal SciPost.
Will rebuild all views to CBVs to use mixing for the recurring
`journal` context variable.

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...

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