Removed trailing spaces.
Fixed variable name.
Pass proper value to order_by_metadata.
Removed undefined variable.
Passes proper value to order_by_metadata.
Added support for combining multiple comment notifications into one.

Instead of getting e.g. three separate notification about three new comments, there's now a single message saying "Foo and 2 other users commented Bar."
Fixed the amount of subject in the notification text.

One of the users is mentioned by name so that user is now correctly excluded from the count of other subjects.
Make sure notification summary exists before using it.