added an intersection visitor that can traverse any group, not only the camera root node

git-svn-id: http://ifcplusplus.googlecode.com/svn/trunk@23 06f6d6f3-f2e0-f239-6e86-ba6a5d17d3a5
added appicon.ico

git-svn-id: http://ifcplusplus.googlecode.com/svn/trunk@24 06f6d6f3-f2e0-f239-6e86-ba6a5d17d3a5