This ease Admin API administration, and also adds checking if qrexec
policy + scripts matches actual Admin API methods implementation.
The idea is to classify every Admin API method as either local
read-only, local read-write, global read-only or global read-write.
Where local/global means affecting a single VM, or the whole system.
See QubesOS/qubes-issues#2871 for details.
FixesQubesOS/qubes-issues#2871