Support SoftwareRequirements

[LourensVeen]

We need to be able to do 'module load' and 'conda activate' before running a CommandLineTool, so that the necessary software is available.

• Study CWL SoftwareRequirements
• Make a sub-syntax for module and Conda, or see what's there already esp. for the latter
• Implement parsing the SoftwareRequirements
• Extend cwltiny to load the software

Since both conda activate and module load modify the environment, probably the best (and certainly the easiest) way to implement this is to generate a shell script and execute that.