HyperlinkedIdentityField now requires View-Name

HyperlinkedModelSerializer sets View-Name on the Fly

* serializers opt class need to be set by serializers Metaclass

 * this is necessary because the HyperlinkedIdentityField 'url' needs to be inserted into base_fields before those get processed to the Serializers.fields attr.

 * BUT it need to happen _after_ opts got initialized. So Metaclass seems best fit for me.