Allow for multi track processing

[wagoodman]

Currently you can do singular groups of parallel/serial tasks. What would be nice is to somehow have a secondary parallel track that runs in parallel to another track. It is not clear how this would be displayed if screen realestate runs out.

Allow a task to have a list of commands that are always run back-to-back in series.

Could be achieved by nested parallel blocks?
Or should there be only one background block allowed?