Singularity installation

In role ohpc_add_rstudio, we install Singularity if it's not installed yet. The old method we used to install Singularity is now unavailable. EasyBuild has moved Singularity easyconfig file to archive. Easyconfig file is still there, moving it to archive means we have to install with fullpath to the easyconfig which is one way we could do. However, install Singularity as module is not recommended. We might want to change the way we install Singularity.