review modles is missing an on_delete positional argument

[standaloneSA]

New generic install from both PyPi and Github result in an error when running

python manage.py runserver:

`
File "/home/bandman/code/findscience/env/lib/python3.6/site-packages/review/models.py", line 22, in

class Review(models.Model):

File "/home/bandman/code/findscience/env/lib/python3.6/site-packages/review/models.py", line 42, in Review

content_type = models.ForeignKey(ContentType)

TypeError: init() missing 1 required positional argument: 'on_delete'
`

[frsilent]

This is the result of Django > 2.0 requiring the on_delete argument. Several changes need to happen for it to work on the latest Django version. I noticed these ones:

• The on_delete arguments set for FKs
• Changing the view to import from django.urls, I'm sure other similarly moved dependencies will need to be changed as well
• Fixing the lazy images reference to user_media
• Changing assignment_tag to simple_tag