Note whether a category was added in a machine readable way

Note whether a category was added in a machine readable way

CategoryMembershipChange is great, but it doesn't have a
machine-readable way to see if the category has been added or removed
from the page. We could parse the comments, but that would rely on
reading the comments and matching the message against the translated
strings.

This patch adds a couple of parameters and notes whether the change
was an addition or removal in rc_params.

Also, puts the evaluation of the AbortEmailNotification hook before
the check of rc_type in the hopes that the extension CatWatch can send
out emails at the right time.

Bug: T175052
Change-Id: I3e2ac0cc148b9d618e2f8b7853b14bff827ee443