Populate project listbox with all owned projects when projectowner textbox is empty. This is a minor UI improvement but needs a lot of work to be done since all SCMHeads depend on the projectOwner field and it is complicated to get rid of that field. We simply need to use the `project` listbox field. It needs to be planned how to do it. One attempt to do didn't work as expected. Take some inspiration from ArgelBargel's GitLab BS.