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/params.rs

@@ -24,9 +24,6 @@ pub struct Params {
 	/// Account start nonce.
 	#[serde(rename="accountStartNonce")]
 	pub account_start_nonce: Uint,
-	/// Homestead transition block number.
-	#[serde(rename="frontierCompatibilityModeLimit")]
-	pub frontier_compatibility_mode_limit: Uint,
 	/// Maximum size of extra data.
 	#[serde(rename="maximumExtraDataSize")]
 	pub maximum_extra_data_size: Uint,