FEAT: Collisional Heating for Neutrals

[aaronjridley]

Is your feature request related to a problem? Please describe.
Collisional heating is being implemented for the ions and electrons. These terms should be mirrored in the neutrals.

Describe the solution you'd like
Create code called neutral_energy_collisions.cpp. Use the energy transferred to the ions and derive energy transferred to the neutrals using the masses, densities, etc. Shouldn't need to actually go through the whole calculation, since it is already done.

Describe alternatives you've considered
Calculate a bulk collision frequency and calculate the ion-neutral friction and heat transfer.

Additional context
Meghan is already working on the ion temperature side, so should coordinate with her.