Add claimAll method

[germartinez]

Add a claimAll() method that transfers all the token balances from the Safe Proxy contract back to the Safe Proxy owner.

[photonite]

Hello Germán Martínez (@germartinez), I am working on Swarm Markets and was wondering if there could be a way to have this feature implemented in a way to be able to include it in the batch transaction, that would really be helpful.

Another thing that would be useful is to be able to transfer ETH to the cpk as part of the batch transaction as well.