add ifc sample file to assimp.

test/models/IFC/AC14-FZK-Haus.source.txt

@@ -0,0 +1,5 @@
+Downloaded from http://iai-typo3.iai.fzk.de/www-extern/index.php?id=1174&L=1 (2013-10-12)
+
+Model made by KIT/IAI (Karlsruhe Institute of Technology / Institute for Applied Computer Science).
+
+Used with permission and fine to redistribute, KIT/IAI would appreciate if the attribution was retained.