Check next/previous path count limit when drawing

[Ermelber]

Problem

Currently it's possible to add more next/previous paths than possible. For example here the tool allowed to add a fourth next item path:

Solution

If a path has already reached the reference limit of 3 next/previous, the tool shouldn't allow linking those paths. Furthermore, the user should also be notified that this operation wasn't allowed, with some error message or tooltip in the viewport.