Changes

• Aggregation & QC workflow now uses gcr.io/aryeelab/bismark docker
• Fixed QC report config that led to an error with recent Pandoc releases
• Changed name of aggregation Bsseq dir and object to 'bsseq' from outputdir_final
• Added aggregate_bismark.wdl workflow to .dockstore.yml
• Added a basic log
• Use default dir instead of /tmp as workdir. (/tmp was used as a workaround for a Mac Docker overmount issue)