Support Quiescent Blockchains
This release adds support for "quiescent" blockchains (only produce blocks/transactions when necessary) to the specification. Normally, Rosetta clients use a tip delay to determine if a blockchain is healthy (i.e. is the current block < 60 seconds old) but this doesn't work for blockchains that can become dormant for some period of time. Quiescent blockchains should populate the NetworkStatusResponse.SyncStatus.Synced field with the sync status so that clients can assess the healthiness of the implementation without relying on the current block timestamp.