Also changes with --genesis-timestamp in chain_plugin:
 * Can only be specified on chain initialization.
 * Utilized for chain initialization even if --genesis-json is not
passed in as well.
 * Adjusts timestamp to nearest block interval even if an explicit
timestamp is passed in rather than "now".

provide an async implementation for incoming::transaction_async , buffer up the retry-able transactions.  EOSIO/eos#3359

chain_id_type should be its own type (without a public default constructor) rather than just a typedef of fc::sha256 #3415

Special exceptions had to be made to `fc::variant::as()const` and
chain_plugin and net_plugin to access the private default constructor.
This is an ugly hack but it works for now. Eventually I need to see if
there is a better solution.

Also the initial public key of the 'eosio' account can now be specified
in CMake rather than specifying the chain ID.

Also fixed --genesis-timestamp bug.

Also return correct error code when database is dirty.

Chain, producer, sql_db and history plugins will now unsubscribe from all controller signals on shutdown to prevent callbacks when neither the plugin NOR the controller is safe to access

Additionally, fixed the logic for max-irreversible-block-age which was only calculating the age when the LIB changed and, fixed a razor-sharp-edge case where producer plugin could shut down with an in-flight boost deadline_timer "success" that resulted in dereferencing a destoyed impl pointer

persisted transactions are the transactions _directly submitted to that node_.  They should only exist on RPC nodes that are accepting transactions from users.  As such the expectation (from our smoke tests at least) is that said node will persist the state of the chain + that transaction until either the block-chain represents the side effects of the transaction OR the transaction expires.

From the pov of the producer plugin, this means that even when speculating on a block the block should include these transactions.

- auto reconnect
- transactions propagate
- fix bugs preventing replay after crash

  - this signal is fired whenever an incoming signal is accepted or rejected and indicates the result
- moved check for stale_production to the block reception code since that now flows through producer_plugin

This partially reverts EOSIO/eos#2750 in favor of always loading the producer_plugin again.  Fix for 85b2948e did not link the default plugin properly.  Also check to make sure that we have not received a block from the future when we attempt to start the next block which is the last symptom before whatever caused the crash in EOSIO/eos#2803