webadmin,userportal: Add AddTabActionButton to exclude-filters.xml

Java classes annotated with @GenEvent, such as AddTabActionButton,
aren't used directly in frontend code. They represent meta-data
processed by GWTP annotation processors, such as GenEventProcessor.
Annotation processors produce additional Java sources which are
used in frontend code, such as AddTabActionButtonEvent.

Change-Id: Ie6424a05d4e76a08bc0d48e5fa299fc7673b718d
Signed-off-by: Vojtech Szocs <vszocs@redhat.com>