Added fields 'anonymous' and 'external' to review Model
Review.delete() now also takes anonymous in account
Merge branch 'hotfix-missing-fixtures-arxiv-testcase' into feature-anonymous-reviews
Added bulk_delete() in review.py
Convert set expression to set literal, removed unused import
Tabs --> spaces
Added visibility choice to ReviewForm
UI hides username if review is anonymous
Cleaned PapersView
Merge branch 'feature-anonymous-reviews'
General cleanup