Allow notifications loop to accept all available parameters.

Previously, the notifications loop accepted only a subset of parameters
from the `BP_Notification_Notification::get()` method.  This made
notification loop filtering very restrictive.

This commit opens up the notifications loop so all parameters are available
as per the `BP_Notifications_Notification::get()` fetch method.

Fixes #5558.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@8761 cdf35c40-ae34-48e0-9cc9-0c9da1808c22