Radiation and Net emission model

[dreamer2368]

Radiation base class and NetEmission derived class is implemented.

• Currently Radiation only has computeEnergySink, which is executed within SourceTerm::updateTerms.
• NetEmission reads tabulated data for net emission coefficient, to run computeEnergySink.
• NetEmission computes net emitted energy based on heavy species energy.
• NetEmission is implemented gpu-compatible.

Minor:

• M2ulPhyS::readTable now generates pointers to DenseMatrix.Read() with specific index of tableHost, instead of using std::vector::back().

How to use:

• specify in the input file as below:

  
  [plasma_models]
  ### currently only takes 'net_emission' or 'none'. default: none
  radiation_model = net_emission

[plasma_models/radiation_model/net_emission]

currently only takes 'tabulated'.

coefficient = tabulated

Input for TableInterpolator

tabulated/filename = 'your_tabulated_file.h5' tabulated/x_log = False tabulated/f_log = True tabulated/order = 1

Minor issue:
- `Radiation::computeEnergySink` is not specified as `virtual`, though it must be. See the issue #184.

TODO:
- If a more sophisticated radiation model requires other than energy sink term, other objects need to have the pointer to `Radiation`. For example, if radiative diffusion is implemented, then `Fluxes` should include the radiative diffusion term in `computeViscousFluxes`.