Add all domain masks to NSCoreServicesDirectory

[pkgdemon]

Creating per discussion from gnustep/tools-make#62

[rfm]

Thanks for looking at this, but you missed how the filesystem layout mechanism works: it's a lot more effort to implement the interaction between gnustep-make, default values, the configuration file etc and the runtime API. When I looked at this I realised that we already had the services variables in gnustep-make but had never completed their implementation by updating gnustep-base.
I have just committed a couple of hours work implementing them; support for the services directory in the filesystem layout for all four domains, so I think we can close this.

[pkgdemon]

No problem. Thank you @rfm I will look over your commit more to see what I missed. It does look a lot more involved than what I thought indeed. Thanks for the help.