Add options to customize heartbeat and max retry interval on Replicator

While testing P2P replication in various scenarios including when the other peers were gone without telling (half close connection), I think it's a good idea to allow users to customize the followings so that the replicators can be more active or aggressive when detecting the errors and retry if they want to.

• Heartbeat Interval : The interval to send the heartbeat to detect whether the peer is still alive. Currently the default is 5 mins.
• Max Retry Interval : The delay between retry. The delay increases exponentially such as 2, 4, 8, 16... seconds. Currently the max delay is 10 mins.