Pull timeline for issues

[stephenmichaelf]

Pull timeline for issues which need it, send info into DbIssuesPopulation interface

@karelz need some clarification on this.

[karelz]

Related to #162 - once we identify that we missed a notification, we can pull it from GitHub Timeline. See my Timeline API experiment in timeline branch commit.

Note that we need latest not-yet-released updated Octokit from AppVeyor CI feed - see details in octokit/octokit.net#1594 (comment) (my commit above used locally fixed Octokit compiled from source)