Verify filters for Corps and Firms

[ianco]

Corps should be filtered based on corp class (XPRO, BC) instead of corp type, as there are some historical corp types we should include (even though they are no longer used)

Confirm we can use MF or FM for Firms.

[ianco]

Firm types are 'SP' (Sole Prop) and 'MF' (Misc Firm)

Corp types are any with corp_class in ('BC, 'XPRO')