Investigate dask support for edge bundling

[amaloney]

Is your feature request related to a problem? Please describe.

See #1384 for a more in depth discussion, briefly this is to investigate adding dask (or more generally paralellism) back to the optimized numba code done by @lmcinnes for edge bundling.

Describe the solution you'd like

• ensure dask speeds up the optimized numba code
• tests
• documentaion
• more in-depth example using both dask and the optimized numba code