flatten incomingMsgObj before calling generateReactions

[michielbdejong]

Since some of the new message formats have nested objects, things became very messy in the SettlementEngine. Also, it now needs to keep some state about outstanding and funding/funded transactions, and the code for that could also do with a little cleanup. Lastly, the integration test for settlements doesn't test the initiateNegotiation function, instead faking it by setting private vars - should clean that up as well.

[michielbdejong]

this will change when creating a small npm module for ledgerloops, see https://github.com/ledgerloops/ledgerloops-webcrypto/issues/4