WIP - multiple companies for users in FMCS

[snipe]

This is still broken, but since it came up again recently, I figured I'd push up what I've already done.

[Toreg87]

@snipe if I understand this correctly this is something I implemented a few years ago: Toreg87@d997a8b
This was rejected upstream but if this seems useful now I can create a new PR. It is currently based on v7 and I am in the process of rebasing it to v8. The scoped locations feature complicates this a bit. I use this in my production site without problems. It could use a little bit love on the UI and is lacking a few translations. But other than that I am quite happy with it.

[snipe]

@Toreg87 I mean, sure! If you can rebase against current v8 and spare me the sorrow, I'd happily take a fresh look at it.