[WIP] Feature/changing parent on relations tab

* https://www.openproject.org/projects/finnlabs-team-2/work_packages/14055/overview

I've implemented the basic behaviour. It slightly differs from the specification in the WP 14055, but it is more consistent with rest of the relations.
@myabc without the id the autocomplete doesn't work. Also, id is used to access the value of the input.