Update all C++ BMI modules to reference virtual destructor

[PhilMiller]

csdms/bmi-cxx#12 has been merged. Now we need coordinated updates of our internal and OWP-wide C++ BMI modules to make sure that they all consistently start to reference the revised definition in clean, atomic steps.

Under the model engine team's purview, there's

• ngen/include/bmi.hpp Update both BMI C++ header copies to reflect virtual destructor #832
• ngen/extern/bmi-cxx/bmi.hxx (submodule from csdms/bmi-cxx)
• sloth/extern/bmi-cxx/bmi.hxx (submodule from csdms/bmi-cxx) Update bmi.hxx to reflect addition of virtual destructor SLoTH#7

Under (I think) the Formulation and/or Soil team's purview, there's references in

• CFE Address BMI header issues impeding other work cfe#122
• SMP Update BMI C++ header to match upstream with virtual dtor SoilMoistureProfiles#17
• SFT Update BMI C++ header to match upstream with virtual dtor SoilFreezeThaw#25
• LGAR-C Update BMI C++ header to match upstream with virtual dtor and correct namespace LGAR-C#26
• PET Rename 'struct bmi' to not conflict with declarations from BMI headers evapotranspiration#38 - not technically the virtual destructor, but gets in the way when I try to make these updates, so it needs to come along for the ride.
• Topmodel Replace BMI_SUCCESS/FAILURE macros with static constants per csdms/bmi-c#12 topmodel#51 also an ancillary change

[PhilMiller]

@nels - I'm calling it a night. Let's talk tomorrow about how to coordinate testing and merging the batch that all need to go together.