enroot is another fully unprivileged container runtime.
New options:
-E option for converting to enroot squashfs image--enroot_file for specifying enroot filenamecc: @TobiasMeisel In this MR I also changed the ogs install location to /usr/local/ogs. Also the ogs binaries are now always in the PATH, no need to specify --app ogs on singularity exec-calls. I will updated the ogs docs accordingly.