Master does not handle InverseOffers in the Accept call (Event/Call API)

InverseOffers are similar to Offers in that they are Accepted or Declined based on their OfferID.

Some additional logic may be neccesary in Master::accept (src/master/master.cpp) to gracefully handle the acceptance of InverseOffers.

• The InverseOffer needs to be removed from the set of pending InverseOffers.
• The InverseOffer should not result any errors/warnings.

Note: accepted InverseOffers do not preclude further InverseOffers from being sent to the framework. Instead, an accepted InverseOffer merely signifies that the framework is currently fine with the expected downtime.