Use jQuery objects in ref dropdown

## What does this MR do?

Keeps the behaviour the same as the ref dropdown, however it now uses jQuery objects to handle the HTML creation instead of passing strings around. It pretty much worked out the box so not much was changed in the dropdowns themselves. Will be easy to transfer this over to other dropdown menus as well.

cc. @jschatz1 @rspeicher @DouweM 

Do we want this to go into a patch release?

See merge request !4850