Move null and zero from kernel space to user space

Created by: Arcterus

This requires changes to several other repos and the addition of the nulld and zerod daemons to implement the removed functionality in user space. I have not yet removed pipe: from the kernel because doing so requires changes to init (as apparently Command in the standard library will always try to open a pipe).

I'd like to transfer ownership of nulld and zerod if possible. (done)