Contributor resolution is not ready for platform support #241

The facade contributor resolution process (augur/tasks/github/facade_github/tasks.py process_commit_metadata) is essentially written solely for github, making it nearly impossible to implement for gitlab, etc without introducing massive code duplication.

heres my migration/rearranging plan for this component:

1. migrate all the github url assembly and API calling/processing to the existing GitHubDataAccess class.
2. Create a new data class AugurForgeUser to act as an internal model/representation of a generic forge-independent user that can be adapted for writing to our db - make sure GitHubDataAccess can return in this format
3. define an interface for the API methods that are needed for contributor resolution, allowing us to use OOP principles to swap out GitHubDataAccess with other classes when we go to add more forges, keeping the remaining resolution logic