[FEATURE] use account monitor

Refactor processes/incoming.js and IncomingPayment Class to use
ripple-account-monitor to listen to incoming payments (GA-599). Also
addresses GA-616.

[FEATURE] Get/Set/Fetch Last payment hash

[TASK] update cli to use updated API

[TEST] Incoming payment class

[TEST] get/set/fetch last payment hash

[TASK] update account monitor to 2.2.0