Allow blank entries in VariantReview edits
Variant create & remove also handles VariantReview
Make VariantPublicationReview intermediate model

Also define the ManyToMany relationship in VariantReview instead of
Variant, because VariantReview is defined to contain user-editable
data (and adding publications is a user edit).
Make sample_data a manage.py command
Merge branch 'master' of github.com:madprime/django-get-evidence

Add readme