We now show inputs for realm details like name, type and URL
in the create_realm.html template opened for "/new" url and
these information will be stored in PreregistrationRealm
objects in further commits.
We add a new class RealmDetailsForm in forms.py for this
such that it is used as a base class for RealmCreationForm
and we define RealmDetailsForm such that we can use it as
a subclass for RegistrationForm as well to avoid duplication.
80b00933b1