Add support for the deadend pieces

[YuriSizov]

Currently paths just abruptly end whenever there is a deadend in the network. A simple solution to that is an introduction of deadend pieces that would be added at such points as is, without any deformation. A more creative solution would be to reuse the same mesh as the ones used for the straights and generate a stump from that.

Not entirely sure how to achieve the latter and would enjoy more control from providing a dedicated mesh from the former, so I'd probably go with that.