Added module support to slurm wrappers

Hi Simon, this is a modification I made some time ago to allow me to add slurm modules in the bpipe config file under the commands section. An example is in the comments in the code. This saves me from having to load all the required modules on the command line before running my pipeline. This also allows me to use conflicting modules in different parts of the pipeline.

Cheers,

Simon Gladman