Provide Docker image

[ajgassner]

should...

• be based on Ubuntu
• check out latest dist release at creation time
• have a configureable cron job to update git data with git2json

[blecher-at]

♥ it!
integrated with travis! and updated readme/homepages

[blecher-at]

If no ssh-key is provided, it should generate one and display it on the console.