Fix contact name update rules

The following rules apply now:
1. "name" column is only updated manually and never over the network
2. "authname" column is only updated over the network and never manually
3. Displayname is a "name" if it is non-empty, otherwise it is "authname".

This fixes a known (pytest.xfail) problem of "name" being changed over
the network when user has set it to non-empty string manually.

This also fixes the problem when "name" and "authname"
became unsynchronized accidentally, when they were equal and then
Origin::IncomingUnknownTo update arrived, setting "name" but not
"authname". Rust regression test is added for this case.

src/qr.rs

@@ -490,6 +490,8 @@ mod tests {
         let contact = Contact::get_by_id(&ctx.ctx, res.get_id()).await.unwrap();
         assert_eq!(contact.get_addr(), "stress@test.local");
         assert_eq!(contact.get_name(), "First Last");
+        assert_eq!(contact.get_authname(), "");
+        assert_eq!(contact.get_display_name(), "First Last");
     }
 
     #[async_std::test]