move exception handling into NFSServerV41 class

as v2, v3 and v4 specs backward compatible with error codes,
merge them into a single utility class. NFSException updated
to print human readable string.

server scope and owners should be configurable and bound to file filesystem and/or dataserver

slotid4 is an uint32. Nevertheless as java does not have unsigned types
we get a negative number in case of bad clients/corrupted packages.

the earlier implementation of reply cache was encapsulated
inside session. On one hand it works, but on the other hand
ugly implementation did not allow me to sleep good.

This patch make nfs server session and cache aware.
The CompoundContext knows about number of operations and
current operation position.

The operation position verification is not spec complaint.
(we set compound status but do not return operation result).
Nevertheless it protects against malicious clients.

remove obsolete class.