Add thread support for GitLab

[shyim]

trafficstars

That would be the way I would solve the thread problem.

After your Okay @orta I can implement also Github too :)

[JoshuaBehrens]

Any activities here? I could need that one :O

[purefan]

pinging @shyim I hope you dont abandon this PR, its good work and I think the review comments are valid

[shyim]

As it took me too long to have it. I just built something similar of Danger for our company.

Free free to create a new PR based on this :)

[uncaught]

@orta I suppose this is superseeded by #1331 and could be dropped?