Migrate duffle driver implementations to cnab-go

[jlegrone]

The driver interface is already defined in the driver package. Many of the driver implementations from duffle are generally useful outside of duffle and should be made available without the need for declaring a dependency on duffle.

[jlegrone]

While the APIs in cnab-go are fairly new, this would also help minimize the downstream impacts of refactors like #28.

[silvin-lubecki]

I agree with moving the drivers here, as it's a main concept in CNAB implementations, and sharing common code between all CNAB runtime clients will reduce interoperability issues 👍