Updated wCCD demo on Testnet

The Concordium wCCD smart contract that is deployed on Testnet has been updated to be natively upgradable. The wCCD tutorial has been updated accordingly. Our wCCD demo dApp on testnet can be accessed here.

Important note: The contract has changed so if you wrapped your testnet-CCD into the old contract then they are now lost. You need to wrap testnet-CCD again.