Support Scaling Each Physics

[pbauman]

Although we are not tied to units in the Physics class, the exception being the reacting flow classes since the thermochemistry libraries are tied to SI units, it might still be useful to have a consistent mechanism to scale/normalize each Physics.

Could maybe be as simple as providing a scaling argument that can be parsed for each Physics? However, it would be nice if the output was rescaled appropriately to not include the scaling to the equations.

Might help alleviate some of the issues that required introducing #319.