(WIP) Trac. #467
wind_movers.py:
- updated so state is copied from correct base class

First draft revision of breaking up Spill object into Release objects
and Spill object. The Spill object now has an attribute called release
which points to a valid release object
- also added serialization capability for Release objects. These
  objects are only used and managed by Spill object. Set up so
  serialization creates a nested object
- reworking __eq__ and __ne__ for objects. Previous approach was to
  compare dict created when to_dict('create') was called. Maybe better
  to just compare attributes as python objects that are used to 'create'
  a new object.

updated tests since many of the old Spill properties are now part of
some release objects. This may change based on code review but this is
current 1st draft implementation.
merged branch test_468 - kwargs to allow different parameters for different distributions
new experiment: LE generation for a 3D plume for use in the model
intercomparison workshop
enhances script for testing netcdf
Experimental Plume Generator: Added ability to set the number of LEs generated over a period of time.  Analysis of new ability.
added error for bad grid current or grid wind file
Merge branch 'master' of https://trac.orr.noaa.gov/git/GNOME2
added a test for bad current file
found bug in RandomVertical - was always passing above mixed layer check
fixed a couple more things in RandomVertical
reflect particle if it moves out of the mixed layer
added a test for the vertical diffusion
Merge branch 'master' of https://trac.orr.noaa.gov/git/GNOME2
added test for vertical diffusion in the bottom layer -- doesn't seem to give the correct answer.
Merge branch 'master' of https://trac.orr.noaa.gov/git/GNOME2 into trac_467

Conflicts:
	py_gnome/gnome/spill.py
(WIP) Trac. #467
working on separating out Spill and Release objects
also refactoring persistence (saving objects)

NOTE: Some tests fail - need to fix these
fixed vertical diffusion so variance is correct
some more tests for the vertical random mover.
Merge branch 'master' of https://trac.orr.noaa.gov/git/GNOME2
added a call to resurface_airborn_elements to the Gnome_Map base class.