User customization of protocols

[mariocj89]

Allow users to define their own protocols that inherit from github.

This should be configuration only and allow to override:

• Token (To be produced via marioc89/github-token)
• API_URL

As an example, a command like:

$ gitorg protocol create
> Choose a base protocol [github]:  github
> API_ENDPOINT: enterprisegithub.mycompany.com/api/v3/
> Do you want to generate a token to access the API? [Y/n]
> Choose a name for your new protocol: ghe

Will allow the user to later run:

gitorg add ghe:myuser

Note, this is a complex issue