Add option to pass additional paths to ogs singularity container call

On linux, ogs6 is executed in a singularity container environment with $ singularity exec path/to/ogs-container ogs path/to/script/script.prj. Here, ogs application searches for the *.prj file inside the container. By default the users $HOME directory is mounted inside the container, so *.prj files in the users home directory are accessible. However, if the *.prj are located outside the home directory (e.g. /work/user-name/.../script.prj) then it is not accessible from within the container as this directory is not mounted in the container by default. It has to be specified explicitly, either in the definition of the container or in the call singularity exec --bind /mypath ...