outdated process model behavior in sipXconfig

I was reviewing Paul's patch (http://track.sipfoundry.org/browse/XCF-2782)
and I accidentally reproduced the problems reported in

http://track.sipfoundry.org/browse/XCF-2766
http://track.sipfoundry.org/browse/XCF-2793

(cannot add or remove the service)

I think that the root of the problem is that sipXconfig is still parsing
the process models located in etc/sipxpbx/process.d directory - and you can
only add/remove processes that are listed there.

Since most descriptor are migrated to new directory (and new format)
process model does not processes, which causes NullPointerExceptions when
we are adding or removing them.

I am not sure if ProcessModel is still needed at all, but if it is we need
to discover list of processes by querying the supervisor and not by reading
local directories.

D.