add firstsuccessful

[samuellsk]

be able to define multiple generators , if the generator is successful , dont continue.

rought sketch
FirstSuccessful {
Filter (And(Not Area(9,On("castle_wall")) , On("floor2")) ,{Remove("floor2") Set("castle_floor2")})
Filter (And(Not Area(7,On("castle_wall")) , On("floor")) ,{Remove("floor") Set("castle_floor")})
...
}

Simply if generator is executed, dont do the others.