Update DRAFT operating company

Updates the configuration of a DRAFT operating company before it is
submitted. Only Opcos in DRAFT status can be edited (400 otherwise).
Changing opco_type re-validates the type-specific person fields for the
NEW type: sole_trader is required (and ubos/directors/signatories
are cleared) for licensed_tpp_sole_trader; ubos, directors, and
signatories are all required (and sole_trader is cleared) for
licensed_tpp_non_sole_trader_private. Returns 404 if the Opco does not
exist or belongs to a different client.