Dummy thermodynamics

[timspainNERSC]

As part of the dynamics integration and testing, we might want to run dynamics-only models, where the thermodynamics do nothing to the ongoing state of the ice.

Modules should be available so that the thermodynamics step does nothing to the state of the model, except for any ancillary data fields that might be necessary.

[timspainNERSC]

The classes implementing the do-nothing thermodynamics are:

• DummyIceThermodynamics for IIceThermodynamics
• DummyIceSpread for ILateralIceSpread

They can be used by adding the config

[Modules]
Nextsim::IIceThermodynamics = Nextsim::DummyIceThermodynamics
Nextsim::ILateralIceSpread = Nextsim::DummyIceSpread

These implementations do not have any configuration options of their own.