Use an interface for logger

[Highstead]

What this does:

Moves from a pointer to a log.logger to a logger interface. I leave in the original code that initializes a default log.logger because this is an older repo and theres no reason to break this.

Why this is necessary

• I have an older repo (orchestrator) that uses martini and the logs are poluted with martini logs that are in a non standard format and make searching them hard.
• Also added support for go modules..