When no arguments are pased to the AppImage, start with
the launcher for a pleasant experience.
Adjust the RPath on our copied osgDB plugins, so that dependencies
are found at the bundled lib dir.
Set OSG_LIBRARY_PATH so our bundled OSG plugins are used by
default.
Reduce which QtQuick plugins we bundle, and ensure we copy libraries
using archive mode to preserve symlinks. Also remove static libs. All of the
above should drastically reduce the image size.
