Dynamics & ice physics overview issue

[timspainNERSC]

• The BBM rheology exists, but is not usable #378
• Tidy up the rheology code #450
• BBMStep uses the MEB::StressUpdateHighOrder() #452
• Free drift dynamics #453
• Using netCDF mesh files in dynamics  #162
• Persisting grid parameters #367
• Implementation fields for advection #337
• Advecting arbitrary fields #99
• Spherical coordinates for the dynamics #463
• Replace dynamics namespaces with classes #467
• Stress advection #468