RMI and SND files were already supported but were missing from the list of
movie & sound menu. Added these in alpha order

	modified:   avmedia/source/viewer/mediawindow.cxx

Change-Id: I3241f1cdd8972fb3da85e8e2bdd26b25f61a53ec
Reviewed-on: https://gerrit.libreoffice.org/3727Reviewed-by: Tor Lillqvist <tml@iki.fi>
Tested-by: Tor Lillqvist <tml@iki.fi>