Messages: Better notification formatting and marking

[r-a-y]

This ticket stems from ticket:5273#comment:33.

It reformats the notification for new messages and clears them when the user visits the actual message thread instead of the message inbox.

Patch also fixes a bug with a user's notification cache not being cleared when a notification is marked as either read or unread.

[boonebgorges]

Is there a reason you're doing this

$text = sprintf( __( '%2$s sent you a new private message', 'buddypress' ), (int) $total_items, bp_core_get_user_displayname( $secondary_item_id ) ); 

instead of this

$text = sprintf( __( '%1$s sent you a new private message', 'buddypress' ), bp_core_get_user_displayname( $secondary_item_id ) ); 

?

I assume it's just a half-finished idea :)

bp_messages_screen_inbox_mark_notifications() should be properly deprecated if you're going to use a different technique for clearing.

A unit test for the failed cache busting would be truly delightful, but is not a deal-breaker.

Otherwise the changes look good. Thanks!

[r-a-y]

In 8202:

Messages: Reformat new message notifications.

This commit changes the single message notification link to go
directly to the message thread in question and not the message inbox.

When the message thread is viewed, new messages are marked as read.

Fixes #5479