Make it possible to use an external installation of iconmath in ICON
It is currently impossible to use an external installation of iconmath in ICON. I don't remember the details but there was something about fortran-support. It was unclear whether we should install it if it is not found at the configure time and a fetched version is used. I think we should install fortran-support together with iconmath to the same prefix in that case. However, we should consider an option, which can be set to ON by default, that the users can set to OFF to disable the fetching and avoid unexpected files in the installation prefix.