Transaction eras (#758)

* Initial groundwork

* A mess.

* Integrate

* Fix tests

* Unit tests

* Tests for unchecked_extrisnic

* fix tab

* Improve binary format.

* fix tests

* Rename extrinsic-pool -> transaction-pool

Closes #770

* Implement unimplemented.

* typo

substrate/core/rpc/Cargo.toml

@@ -13,7 +13,7 @@ parking_lot = "0.4"
 parity-codec = { version = "1.1" }
 substrate-client = { path = "../client" }
 substrate-executor = { path = "../executor" }
-substrate-extrinsic-pool = { path = "../extrinsic-pool" }
+substrate-transaction-pool = { path = "../transaction-pool" }
 substrate-primitives = { path = "../primitives" }
 sr-primitives = { path = "../sr-primitives" }
 sr-version = { path = "../sr-version" }