[dask] Make vanilla-pad work properlly with dask

In this MR, I'm.

1. Wrapping the pipeline with DaskWrapper, because it wasn't. I think that's why things were not working for you with SGE @ydayer. vanilla-pad was creating SGE jobs AND running everything locally.
2. Added the options "--dask-partition-size" and "--dask-n-workers", so the user has some freedom to set these parameters if the heuristics in place are unpleasant.

I'll merge this one right away because of the workshop.

Feel free to open issues if any

merged

mentioned in commit 61e5267b

resolved all threads

mentioned in issue #37 (closed)