Add support for github and options to filter by group/orgs and users at remote git level

[mborne]

• Add Git\GithubClient and Git\GithubProject
• Detect github.com domain to create the corresponding client throw a ClientFactory
• Add option --orgs and --users invoking the correct API (https://api.github.com/users/mborne/repos or https://api.github.com/orgs/symfony/repos)
• Support --orgs and --users option for GitlabClient
• Move git relative code to MBO\RemoteGit namespace to prepare further project split
• Review options and mark some as deprecated due to orgs and users introduction at API level #29 - Prepare option review (orgs and users will be more efficient than some of them)
• Move out MBO\RemoteGit to mborne/remote-git