[MOD] Introduce mark all as read for notifications

git-svn-id: file:///var/local/code.tiki.org/tikisvn/trunk@49771 b456876b-0849-0410-b77d-98878d47e9d5
[MOD] Allow to clear individual notifications from the unread list

git-svn-id: file:///var/local/code.tiki.org/tikisvn/trunk@49772 b456876b-0849-0410-b77d-98878d47e9d5