Nonce issues

[ineiti]

The use of nonces is not optimal for the moment:

• the pool-client in core/txn/pool/controller/action.go just increases the nonce by 1 every time Sync is called. Instead it should request the current nonce from the blockchain
• the transaction check in core/validation/simple/simple.go allows for some leeway in Service.Accept, whereas the Service.validateTx only allows correct nonces. IIUC, the validateTx should also accept the same leeway, else it will not work. Even better, the system should not need the leeway. I'm not sure if it actually orders transactions so that the nonces are correct. Probably it just discards wrong nonces