Load modules in scripts, instead of ahead-of-time

Tested this out on today's NextSeq flowcell, seemed to work out alright. No modules loaded on command line, all done by the various scripts, so I can't forget to accidentally load them anymore. :smile:

I noted in the commit message for 4d8f544 that it may be better to put the module-load responsibility into create_processing.py - still not entirely convinced one way or the other.

Requires that $MODULELOAD is set.