Adding ability to drop old issues on new review.
When a user publishes a new review request, all bots re-run and open new issues. If the publisher didn't fix the old issues (maybe they just added a new file) they now have double the issues, half of which are duplicates. The bot should be responsible for dropping the old issues, if it is configured as such.
This change adds support for configuring each bot to drop old issues when a new review request is published. All changes are done server-side for better performance (closest to the database) and better user experience (issues dropped as soon as extension is executed).
Note this change also changes the service_id to be based off the configuration name. (This is required so that the same tools configured 2 different ways doesn't drop the other's issues).

Review with previous issues:

   - Post new review with issues fixed -> Drops old issues. (*)

   - Post new review with issues not fixed -> Drops old issues

Review with no previous issues:

   - Post a new review with issues -> Opens new issues.

   - Post a new review without issues -> Still passing, doesn't drop anything.
Two configurations using the same tool, one dropping old one without:

   - One tool drops its old issues, the other doesn't.
In all cases:

   - Only dropped issues when box was checked

(*) - We might think of a better solution to this. If the user fixes the issues, by the time they publish the new review, the old issues will be "dropped" instead of "fixed". That might be OK (mark the issues fixed before you repost?). I'd like to avoid having to semantically deduce if the issue was "fixed" or dropped. (Maybe they just moved everything down a line).