adds a milestoned event

[rauhryan]

captures the milestoned event and publishes it to the client as an edited event

https://developer.github.com/changes/2016-10-27-new-label-and-milestone-webhooks/

[dahlbyk]

We also need to handle demilestoned.

I noticed this new job is identical to issues_edit_issue_job.rb. Is there a base job they could inherit from?

Also, what's relationship between this new job and issues_assign_milestone_job.rb?

[rauhryan]

@dahlbyk yeah, you are right.

I looked into it a little closer

I thought I could just shovel the event to a generic edited handler but we don't handle that event client side yet.

So, I thought I'd future proof it a little bit.

Added a method to the job resolver to t conventionally resolve webhook event jobs and if one can't be found it will fallback to the issues_edit_issue_job

Should be generic enough to catch things if new events pop up in the future