Make referee filtering conditions on unavailability and conflict of interest as "opt-in" instead of "opt-out", diverting costly queries to the "non-default" option.

possible fix for #360

An empty invitation is no longer created when the referee is marked as unavailable

Use the same method to determine authorship claims across pool and claims page. Fix bug where pool was hiding submissions without ability to make a claim on them.

Inform EIC that an editorial recommendation for revision must be formulated before the authors are allowed to resubmit

fixes #354

fixes #353

author profiles are explicitly deleted and recreated as exact copies

use annotated fellow queryset to defeat N+1 problem

fixes #346

reword assignment stage update email
disable automatic withdrawal after assignment deadline

fix refereeing reminders not being sent