Improve physical consistency and detail in heat source specifications

[ejfdickinson]

@ikorotkin wrote:

for the future releases of BPX, would you consider defining all the heating terms in the DFN model according to their derivation from the Newman model itself and the conservation law (as in G. Richardson at al. "Heat Generation and a Conservation Law for Chemical Energy in Li-ion Batteries")? Even if not, your opinion about it and its real-world application would be extremely useful! The reason I am mentioning this work is that the definition in BPX does not take into account the heat dissipation in particles, which can be significant for relatively high C-rates. It is also consistent with the DFN model.

[ejfdickinson]

I would support this consideration as an activity for a BPX subcommittee at v1.x stage!