Allowing users to see more notification types (Bug #1382899)

Adding a get_special_notifications function to allow for the adding of
special case notification options to non admin user's notifications list

Allowing the 'Objectionable content in forum' notification type to be
seen/set by forum moderators/admins

Change-Id: I69ab8b9de850345868346a85342f48d1f0b0f2aa
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>
Merge "Allowing users to see more notification types (Bug #1382899)"