Models: sqw_spinwave: use Process to distribute over cpu's

[farhi]

The Process class should be used in the 4D case to speed-up computation:

• distribute the 'ie=1:tuu' loop into asynchronous computations into separate directories
• wait for all processes to end (waitfor)
• collect and merge data sets

this will then 'emulate' an MPI execution on local-host

NOTE: a simple implementation would use as many threads as the 'tuu' number, independently of the real CPU capability.