Generalise teleport to teleport-to-actor

[Mikolaj]

Probably only a variant that does not need extra UI, because pointing with mouse at small letters with no feedback is error-prone and another option, modal dialogs for selecting another actor, get newbies confused. The simple variant would teleport one actor to a random position that is maximally close and adjacent to the other actor involved in teleport. Let's see if any other effect can be generalized similarly and try to share code.

This ticket should be easy, but I may be missing something and so perhaps it's not completely self-contained. Also, sample content that uses it will require some work.