IEP-83 Thin Client Keepalive (heartbeat)

Igniters, Please review the proposal to add heartbeat messages to the thin client protocol (both 2.x and 3.x) and let me know your thoughts: https://cwiki.apache.org/confluence/display/IGNITE/IEP-83+Thin+Client+Keepalive

Unmarshalable result from the MX beans

    Hi, Igniters.     We've found that invocation results from some MX beans might not be properly represented on clients like jconsole [1]. In the exception cases. We pass Ignite exceptions or JMException with Ignite exception causes to the client. And the client fails to unmarshal unknown e