IEP-83 Thin Client Keepalive (heartbeat)

[Pavel Tupitsyn]

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