Refactor CCPClearingMechanism #40
Description
Refactor CCPClearingMechanism to introduce a novate method that takes a FillLike between some askTradingRef and bidTradingRef and returns two new FillLikes between self and askTradingRef and bidTradingRef.
Also have CCPClearingMechanism create a child BilateralClearingMechanism actor which can then be used to process newly created FillLikes.