webadmin: refactoring in SplitTable

Replace terms which indicate directions and locations with other terms
that indicate actions and types of entities, so they will be suitable
for vertical split table as well:
top -> excluded
bottom -> included
down -> include
up -> exclude

Change-Id: Id6f0452019798e284693df96fc731d5836fbe2dd
Signed-off-by: Arik Hadas <ahadas@redhat.com>