"Send reminder" functionality

[ianshward]

For the future backlog - for tasks that create GH issues to track a team member's progress on completing an action, especially those where we want dispatch to track state as to who has and has not taken an action when doing so is otherwise impossible to track from some other data source we have access to, we could have a remind CLI command which would work like:

• $ remind "title of issue" "text of reminder"

• dispatch-remind looks up all the GH issues open that match the title
• dispatch-remind posts a reminder comment to remind folks they still need to complete the action

[k-mahoney]

In a similar vein, it would be great if dispatch could comment on the issue when an alert has been escalated to PagerDuty.