Use and test own code for adding email

It provides form validation with better feedback.
Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/accounts/tests.py

@@ -229,9 +229,16 @@ class RegistrationTest(TestCase, RegistrationTestMixin):
         )
         self.assertContains(response, 'Register email')
 
+        # Try invalid address first
+        response = self.client.post(
+            reverse('email_login'),
+            {'email': 'invalid'},
+        )
+        self.assertContains(response, 'has-error')
+
         # Add email account
         response = self.client.post(
-            reverse('social:complete', kwargs={'backend': 'email'}),
+            reverse('email_login'),
             {'email': 'second@example.net'},
             follow=True,
         )

weblate/html/accounts/email.html

@@ -10,7 +10,7 @@
 {% show_message "error" _("Please fix errors in the registration form.") %}
 {% endif %}
 
-<form action="{% url 'social:complete' "email" %}" method="post" accept-charset="utf-8">
+<form action="{% url 'email_login' %}" method="post" accept-charset="utf-8">
 
 <div class="panel panel-primary">
   <div class="panel-heading"><h4 class="panel-title">{% trans "Register email" %}</h4></div>