Allow changing water Level of Interiors behaving like exteriors
OpenMW and Morrowind don't allow changing the water level when the interior cell behave like an exterior one. Allowing that will open new scenarios like simulating tides in islands or running for your life through a sinking ship.
(RM-3244 from redmine: created on 2016-03-11 by Amenophis ., , closed on 2016-03-12 by scrawl .)