edumanage.admin: Formsets and validation for Name, Address, URL inlines

[zmousm]

Fix #77

• edumanage.forms: Subclass URL_i18nForm, i18nFormSetDefaultLang, URL_i18nFormSet with valid_urltypes, obj_descr class attributes for every use case
• edumanage.views: Replace partialclass() with above use-case specific form/formset classes
• edumanage.admin:
  • Override django.contrib.contenttypes.GenericTabularInline.get_formset() so as to have validate_min passed to generic_inlineformset_factory()
  • Reorganize inline classes and extend with form, formset, min_num, validate_min, so as to perform formset validation as appropriate
  • Add missing address inline to Realm