Tidy up models file

[lili2311]

• remove created_at field from cafes https://github.com/womenhackfornonprofits/we-meet-django/blob/master/london_cafes/london_cafes/models.py#L45 this is not needed
• Remove address as it's own model as it is not needed instead move address1, address2, city and postcode as part of the cafe model.
• Remove atmosphere, coffee and wifi models as they are just ratings. So each one should simple be a reference to a rating as a foreign key.
• make migrations and migrate the database and commit the migrations in this PR

[gnocchi2815]

Working on this

[gnocchi2815]

First two bullets covered in issues 62 and 64. Working on the ratings bullet point.