Feature: Uni-directional reflection.

[dzatoah]

In order to be able to use mdns-reflector in our schools (Debian Edu), we need the option to announce the services unidirectionally from one network to the other and not arbitrarily bidirectionally (like right now).

I will provide patches for this and ideally we find a solution that pleases us both and they can be merged into this Repo.

[sunweaver]

@vfreex Do you see any blockers for implementing this?