change unit of emissions token from tCO2e to kgCO2e

[sichen1234]

The emissions token is by itself unitless, but by convention we chose tons of CO2e before because the US EPA eGRID database's utility emissions factors were in tCO2e. Now looking at other applications, kgCO2e is more typical and manageable, so we will change the standard to be kgCO2e going forward.

This does not require changes to the emissions tokens contracts but rather to the emissions factors that are loaded.

[sichen1234]

This has been fixed for the way the supply-chain/ and scope 3 emissions tokens are calculated.

Still need to change the data loaded for the utility emissions factors and those calculations, when we get to them next.