Implement PullFromGitHub to grab data from GitHub

[stephenmichaelf]

This is a parent ticket to track the following:

• Implement WebHook into GitHub notifications - Implement WebHook into GitHub notifications #161
• Identify missed notifications - Get delta of GitHub notifications #162
• Pull timeline for issues with missed notifications - Pull timeline for issues #164

[karelz]

Updated text above, keeping issue links as #xyz, otherwise they don't link properly ...