Rework user profile settings

Accessibility:

- improved semantic layout
- Fixes unlabelled input for custom pronouns. CC @hazy
- Adds labels to dropdowns.
- Shortens certain texts for less verbose screen reader outputs and
  people with slow reading speed.
- Turned optional username rename helper text with low contrast into
  "normal" help text.

UI/UX:

- Removes section about primary email which is no longer managed in the
  profile section.
- Fixes section about primary email not displaying in user settings when notifications are
  not available.
- Removes primary email display, because it is not actually a form
  element here. (Alternatively, we could display it and link to the
account settings for managing the email)

tests/integration/auth_ldap_test.go

@@ -185,7 +185,6 @@ func TestLDAPUserSignin(t *testing.T) {
 
 	assert.Equal(t, u.UserName, htmlDoc.GetInputValueByName("name"))
 	assert.Equal(t, u.FullName, htmlDoc.GetInputValueByName("full_name"))
-	assert.Equal(t, u.Email, htmlDoc.Find("#signed-user-email").Text())
 }
 
 func TestLDAPAuthChange(t *testing.T) {