holding that direct arranger liability under CERCLA may be imposed against corporate officer or director if, under totality of circumstances, he or she had authority to control and did in fact exercise actual or substantial control, directly or indirectly, over arrangement for disposal, or for off-site disposal, of hazardous substances

stating that acrimony is cause to appoint a trustee "when the inherent conflicts extend beyond the healthy conflicts that always exist between debtor and creditor or ... when the parties ‘begin working at cross-purposes’ "