Save 'issue reopened' event into the DB

As a gh-backup user
I want to be able to see the status of an issue as I would on github
So that I navigate easily to the content I want

We are currently not tracking the event of when an issue is reopened. In order for our app to reflect github's information we should include this.

- [x] Receive webhook from gh when an issue is reopened
- [x] Save this data to the relevant issue on the issues table
- [x] Determine whether we wish to display this update in the UI somewhere

The structure for doing this issue has already begun in `controllers/event_type.ex` but has been commented out as it is incomplete. Look for the reference to this issue in that file.