Use EPA-CEMS crosswalk to calculate total emissions by plant (or generator) prime mover fuel

[aesharpe]

Context:

Based on the SOW defined here

The changes will take place in RMI's UTH repo, not this repo, but this is documented here for planning purposes.

This epic goes hand in hand with getting the new EPA crosswalk integrated into PUDL #1123

Description:

There are two main phases of this epic:

1. Check that the current code done by @TrentonBush last fall is still executable given changes to RMI's input data. Change the code as necessary, prioritizing accessing data via pudl.

2. Pick up where @TrentonBush left off and add more analysis code