Centralize location of workflow versions

Workflow versions are kept in three different files, workflow.js, metagenome_pipeline_wdl.tmpl and nmdcEDGE_assembly.wdl. This makes it more likely that a workflow version will be updated in one file but not in the others. I'm going to move all workflow versions to workflow.js and use pipelineMonitor.js and workflowMonitor.js to fill in the wdl file version at runtime