Extend SCIR libraries to support memory requirements

[prioux]

The SCIR (Simple Cluster Interface in Ruby) class and subclasses provide an interface to a cluster's scheduling system.

It currently supports clusters of many different types, SGE, Slurm, PBS, Moab, UNIX processes, LSF, etc etc.

Its job object model allows the user to specify things like the location of stdout and stderr file, job walltime, etc.

It does not support providing a memory requirement, however. In the past we've always handled this by having the admin configure a direct command-line option for the sbatch or qsub command with the extra_qsub_args string option.

Add a new memory parameter (value in whole megabytes?) to the job object and make sure all the subclasses can add the associated resource limit at launch time.

[prioux]

Needed for a new tool with dynamic memory requirements that Natacha is working on.

[prioux]

Implemented in b6a383a