Removed the managed tx state from the chain manager to the transaction
pool where it's much easier to keep track of nonces (and manage them).
The transaction pool now also uses the queue and pending txs differently
where queued txs are now moved over to the pending queue (i.e. txs ready
for processing and propagation).

* Changed CalcGasLimit to no longer need current block
* Added a gas * price + value on tx validation
* Transactions in the pool are now re-validated once every X

Transactions will be invalidated when the tx.gas_limit > block.gas_limit

Transactions are now propagated to peers from which we have not yet
received the transaction. This will significantly reduce the chatter on
the network.

Moved new mined block handler to the protocol handler and moved
transaction handling to protocol handler.

Implemented a new transaction queue. Transactions with a holes in their
nonce sequence are also not propagated over the network.

N: 0,1,2,5,6,7 = propagate 0..2 -- 5..N is kept in the tx pool

All nonce error handling has been moved to the worker

The transaction pool will now some easily be able to pre determine the
validity of a transaction by checking the following:

* Account existst
* gas limit higher than the instrinsic gas
* enough funds to pay upfront costs
* nonce check

Transaction pool will attempt to ignore invalid transactions it had
previously encountered.

* chain manager sets td on block + td output w/ String
* added tx pool tests for removing/adding/validating
* tx pool now uses a set for txs instead of list.List