Changeset discussion feature

New ChangesetComment model and join table between users and changsets for comments subscriptions
Made commeting changesets possible via "browse" interface
Comments feed for all changsets, particular changeset
Email notifications of new comments on "subscribed to" changesets
That looks bogus - you have a ternary operator with one branch returning an array and the other returning a boolean. Suggest the else should return an empty array, or perhaps more likely `nil`. In fact I'd suggest writing it in a much more readable way as:

```
@comments = @changeset.comments.includes(:author) if params[:include_discussion].presence
```