Emissions: Support custom EFS and FEPS EF overrides

[ ] support overrides for specific EFs when using FEPS; this can be implemented without requiring updatres to eflookup by one of the following ways:
- Instantiating eflookup.lookup.FepsEFLookup and then apply overrides specified in the bluesky config (it's based on a dict, which can be easily updated
- Instantiating eflookup.lookup.BasicEFLookup with a EF dict specified in the bluesky config
[ ] support specifying EFs from scratch (using eflookup.lookup.BasicEFLookup); could use model basic

pnwairfire / bluesky