This change siplifies the structure of the simulation parameters,
removing the gnpy.science_utils.simulation layer, provides some
documentation of the parameters and define a mock fixture for testing in
safe mode.
Jan: while I'm not thrilled by this concept of hidden global state, we
agreed to let it in as a temporary measure (so as not to hold merging of
Andrea's flexgrid/multirate patches). I've refactored this to a more
pytest-ish way of dealing with fixtures. In the end, it was also
possible to remove the MockSimParams class because it was not adding any
features on top of what SimParams can do already (and to what was
tested).
Change-Id: If5ef341e0585586127d5dae3f39dca2c232236f1
Signed-off-by: Jan Kundrát <jan.kundrat@telecominfraproject.com>
