Basic Authority (#991)

* Firt commit.

* First non-functional but correct implementation of BasicAuthority.

Still needs:
- Sealing infrastructure.

* Punch a hole to give miner access to key store.

* Fix test built.

* Basic version of synchronous mining.

This will seal a block whenever a new transaction comes through.
To be made better we need a timer which will wait for one second after the
last block before sealing a new one - better still would be to cooperatively
interleave blocks with other sealing nodes.

* Add tests.

* Fix minor issues from repotting.

* Address grumbles.

json/src/spec/spec.rs

@@ -57,13 +57,13 @@ mod tests {
 	"engine": {
 		"Ethash": {
 			"params": {
-				"tieBreakingGas": false,
 				"gasLimitBoundDivisor": "0x0400",
 				"minimumDifficulty": "0x020000",
 				"difficultyBoundDivisor": "0x0800",
 				"durationLimit": "0x0d",
 				"blockReward": "0x4563918244F40000",
-				"registrar" : "0xc6d9d2cd449a754c494264e1809c50e34d64562b"
+				"registrar" : "0xc6d9d2cd449a754c494264e1809c50e34d64562b",
+				"frontierCompatibilityModeLimit" : "0x"
 			}
 		}
 	},