Added SLURM support.

Also cleaned up some unused code and fixed an output message in
multicore loading.
Added documentation for SLURM.
Handle snpEff/VEP specification checking in gemini_main via choices.
Remove --lsf-queue --torque-queue, etc options for loading.

Added a --scheduler and --queue option instead. This allowed
some argument validation logic to get moved to gemini_main, where
it should be.