Re-introduce contract logging.

[rkeene]

Follow up to #212:

Logging was removed from contract.go in f0d65c0. Maybe that logging can be re-introduced ?

[iwasaki-kenta]

Logging will be re-introduced once the logging system has been partially refactored in the coming week.

[samsends]

Just checking in, whats the status on this?

[rkeene]

@sbsends We're still planning on re-introducing this logging but have not finalized how it will be done.

[samsends]

@rkeene could I pick up the logging if no one else is working on it?