Pass additional filter arguments to legacy forum content filters.

In particular:
- the bbPress 1.x topic object
- the BuddyPress group object

are passed.  This allows plugins to better customize the activity
content before the bbPress 1.x forum post is recorded in the activity
stream.
Add subscription type to non-AJAX selectable subscription types.

The following options:
- Self-notifications
- Manual subscriptions to a topic
- Replies to topics you started
- Replies to topics you have replied to

Are not passed to $group_status in ass_group_notification_forum_posts().

This commit passes these subscription types.
Refactor 'bp_ass_forum_notification_message' filter.

Instead of passing multiple arguments to the filter, this commit
consolidates these arguments into an array.