Corpses don't disappear

In Morrowind, corpses eventually disappear. In OpenMW, they stay forever.

Per Scrawl, this is "related to unimplemented fCorpseClearDelay".

(RM-2363 from redmine: created on 2015-02-11 by Gordon Hales, , closed on 2016-02-28 by scrawl ., relates #2467 (closed), blocks #2369 (closed))