feat(templates): the shared form and delete pages in a centred column

The pages many views share were a horizontal form whose Cancel went
back in a primary colour beside a green Save, and a delete question in
a yellow alert squeezed into half the width, which wrapped word by word
on a phone.

Both now sit in a centred column with their heading: the form's fields
with their labels above in a card, Cancel outlined and Save the primary
action; the delete page asks "Delete <name>?" in a card with a red
edge, says what deleting does, and offers Cancel and Delete.

The form for a user's rights on a VM names them as the VM's Users tab
does: Change settings, Delete the VM, and Change console settings,
which only counts together with Change settings.

webvirtcloud/tests/test_delete_pages.py

@@ -34,7 +34,7 @@ class DeletePageTests(TestCase):
         self.client.force_login(admin)
         for url, consequence in pages.items():
             with self.subTest(url=url):
-                alert = html.fromstring(self.client.get(url).content).xpath("//div[contains(@class, 'alert-warning')]")
-                self.assertEqual(len(alert), 1)
-                self.assertIn(consequence, alert[0].text_content())
-                self.assertNotIn("Are you sure", alert[0].text_content())
+                card = html.fromstring(self.client.get(url).content).xpath("//div[contains(@class, 'border-danger')]")
+                self.assertEqual(len(card), 1)
+                self.assertIn(consequence, card[0].text_content())
+                self.assertNotIn("Are you sure", card[0].text_content())