Create upgradeable contracts.

[rashtrakoff]

The contracts currently aren't upgradeable. Multiple bugs have been found and should some bug be found on mainnet version, it will become very difficult to fix and deploy a new set of contracts and tell all the users to change their streams. Although upgradeable contracts are controversial, particularly in our case as we intend to keep the control to ourselves initially, it would be helpful in having a set of upgradeable contracts which we can deploy when we choose to hand over the reigns of the project to the community.