Make homogenization optional

[samwaseda]

Since homogenisation always has the same arguments, I made them optional.

Before:

homogenization = pr.continuum.damask.Homogenization(method='SX', 
                                                     parameters={'N_constituents': 1,
                                                                 "mechanical": {"type": "pass"}})

Now:

homogenization = pr.continuum.damask.Homogenization()

And as always, you can still use the earlier commands.