[Feature] vlink support

[caiot5]

VLinks were a common practice on late 90s and early 00s where you could add "virtual links" to your additional domains to be shown at /LINKS instead of having to do the actual link. Several IRCds implemented the feature at that time, PTLink (core) and Unreal (module) being the most remarkable ones.
It was quite useful specially when you merge networks and the merged network had their domains which would be replaced due to standardization but the user can still see them on /LINKS. I would really appreciate that.