Convert radios in edit org type page (basic)

Changes the OrganisationTypeField class used by
OrganisationOrganisationTypeForm.organisation_type

OrganisationTypeField is also used by the forms in
/add-service:
- CreateServiceForm
- CreateNhsServiceForm

Because of that, this commit also includes changes
to the template for that route.

Note: this also moves where OrganisationTypeField
appears in app/main/forms.py so it can use
GovukRadiosField.

app/templates/views/organisations/organisation/settings/edit-type.html

@@ -1,4 +1,3 @@
-{% from "components/radios.html" import radios %}
 {% from "components/page-footer.html" import page_footer %}
 {% from "components/page-header.html" import page_header %}
 {% from "components/form.html" import form_wrapper %}
@@ -15,7 +14,7 @@
     back_link=url_for('.organisation_settings', org_id=current_org.id)
   ) }}
   {% call form_wrapper() %}
-    {{ radios(form.organisation_type) }}
+    {{ form.organisation_type }}
     {{ page_footer('Save') }}
   {% endcall %}
 {% endblock %}