Deep Github intergration - Changelog

[alrik]

As a software maintainer I want to connect my github repositories to release-notes, so that all updates to my changelog or release-notes definition get automatically published to the hub.

Acceptance Criteria:

• Connect existing release notes with github repo
• Create new release notes from github repo
• Select branch to check for updates, (default master)
• Read notes from release-notes.yml file, fallback to CHANGELOG.md