Add check on latest_block_time

[george-aj]

Problem A node can be catching_up:false yet when /status? is inspected the latest_block_time can be behind the current time.

Symptoms This causes issues when trying to monitor missed blocks, since the node doesn't get updated, neither does the missed block counts, but yet the cosmos/slashing/v1beta1/signing_infos query will return a response as if the node was caught up.

Solution Check that the latest_block_time is within the stalled_minutes amount and if not don't use it as an RPC node and report it as down/not synched.

[dylanschultzie]

This might pertain to this issue as well:

https://github.com/blockpane/tenderduty/issues/45