Harden messages against replay attacks

[konradkonrad]

Depending on the value of self.asset, messages could be re-applicable between two instances of the same state channel (between=[Alice, Bob], asset=BBCoin). Given that:

• Alice and Bob opened+settled channel for BBCoin yesterday AND
• Alice and Bob open a new channel for BBCoin

If self.asset resolves to the same value, there seems to be no value unique to the current instance, i.e. yesterdays messages could be valid in today's channel.

So: either the asset-address needs to be unique, or we should include the state-channel address in signed transfer messages.

See:
https://github.com/brainbot-com/raiden/blob/master/raiden/messages.py#L291
https://github.com/brainbot-com/raiden/blob/master/raiden/messages.py#L394

[czepluch]

This should be taken care of with #93 that will introduce nonce ranges.

[czepluch]

This can be closed with #287 that add nonce ranges and #211 that makes sure that the same lock cannot be unlocked twice.