* Adjust opened issues count in the milestone burndown chart
to match current opened issues in the milestone.
* Fix completion rate calculation to include milestones only.

Adds `# frozen_string_literal: true` to spec/models ruby files

Display only labels and assignees of issues
visible by the currently logged user
Display only issues visible to user in the burndown chart

Previously, this would include the entire User record in the update
hash, which was rendered in the response using `to_json`, erroneously
exposing every attribute of that record, including their (now removed)
private token.

Now we only include the user ID, and perform the lookup on-demand.

This reverts commit 13e37a3e.