[Enhancement] Add another plus button for appending an entry to the end of a "Multiple" type predicate

[DorkOrc]

There is no [+] button at the end of the list to add another predicate for the "Multiple" type, so you end up needing to prepend and then painstakingly shift it down one by one.

This is also present in some places and not in others but I don't remember where exactly off the top of my head, so might be worth going through and adding this in other places where it is missing too.