Redesign forms, verify link ownership with rel="me" (#8703)

* Verify link ownership with rel="me"

* Add explanation about verification to UI

* Perform link verifications

* Add click-to-copy widget for verification HTML

* Redesign edit profile page

* Redesign forms

* Improve responsive design of settings pages

* Restore landing page sign-up form

* Fix typo

* Support <link> tags, add spec

* Fix links not being verified on first discovery and passive updates

app/views/auth/confirmations/finish_signup.html.haml

@@ -8,7 +8,8 @@
         = msg
         %br
 
-  = f.input :email
+  .fields-group
+    = f.input :email, wrapper: :with_label, required: true, hint: false
 
   .actions
     = f.submit t('auth.confirm_email'), class: 'button'