ModelSerializer works much simpler with Angular Django REST Resource due to the way URLs are constructed.

For blacklocus/angular-django-rest-resource#5.
Simple forms for testing deletion and creation.

For blacklocus/angular-django-rest-resource#5 and testing blacklocus/angular-django-rest-resource#10.
A couple of interesting plants.

For blacklocus/angular-django-rest-resource#5.
Add `$update` action, make `$save` use `PUT` HTTP method when id field is set.

For $save, this assumes that `ModelSerializer` is being used and supplying the primary key of objects as the 'id' field. If a different field name is used, the developer would have to override the save action's method_if_field_has_value setting.

Fixes blacklocus/angular-django-rest-resource#10.