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.

Filtering is done by new template filter. Checking the position
of the current item in the forloop.

Certain actions, such as looking into the editorial page, were
 possible to do by (possible) authors. All submission views
 related to the EdCol are now filtered by the get_pool filter in
 the SubmissionManager to exclude objects with the requesting user
 being a (possible) author.