Introduce GitHub integration

[andreiruban]

As kotbot
I want to provide push-notifications about GitHub repo activities of chat participants
So I informing chat/community members about open pull requests, branch merging and other kind of activities

• API design
• Integration with GitHub API
• push implementation

Suggested commands:

• github_authorize - connects to GitHub
• add_github_repo - adds repository to push list
• remove_github_repo - removes repository from push list
• list_github_repos - lists all added repositories