deal manager secondary trades

[Detoo]

TODO

• Contract size too large. Will move stuff to storage
• Review aginst specs and add more tests
• All interfaces are placeholders for unit-test purposes (i.e. method names are not final)

Updated

• Spec: decided not to extend LexScroWLite with secondary trade logic because the overlaps between primary and secondary trades turns out to be too small to worth sharing the same base contract
  • The underlying NFT pathways are very different. If we implement both inside LexScroWLite, they will be mostly non-overlapping if...else branches. Why risking re-audit LexScroWLite if most of its codes are re-written?
  • However, secondary trading logic will still live on DealManager through a dedicated storage SecondaryTradeStorage; this way we don't need to deploy a new manager (and its factory)