add example NFT forwarder, with tests

[phouse512]

adds an NFTForwarding contract that allows for an owner to redirect NFTs to another recipient. closes issue #10

• adds create_forwarder.cdc transaction for creating forwarder object with recipient as argument
• adds TokenForwarding.cdc contract that holds NFTForwarding contract, which implements the Receiver interface
• adds lib/go/test/forwarding_test.go and utilities to help test forwarder in action

[phouse512]

I'm not sure why the builds haven't been running - let me know if there is anything I need to do to fix that

[satyamakgec]

Closing this PR in the favour of #116