Job schedulers and resources requested

Currently three job schedulers are supported: LSF, PBS and SLURM, defined by the environment variable JOBSCHEDULER. For LSF and PBS, jobs are submitted as single job scripts. For SLURM using launcher.

A common problem under LSF is that jobs are too long in pending status. This happens because no jobs slots with the requested resources are available. The wait times can be reduced by minimizing the walltime and memory requirements.

Lets add info here how this is to be done.