Extract some parts of miner from ethcore. (#7353)

* Move miner away from ethcore.

* Fix ethcore to use miner/transaction.

* Fix tests and warnings.

* fixed incorrect merge of the test in the documentation

ethcore/light/src/net/mod.rs

@@ -18,7 +18,7 @@
 //!
 //! This uses a "Provider" to answer requests.
 
-use ethcore::transaction::UnverifiedTransaction;
+use transaction::UnverifiedTransaction;
 
 use io::TimerToken;
 use network::{HostInfo, NetworkProtocolHandler, NetworkContext, PeerId};