WIP: Dask connector

[martindurant]

cc @avaranovich
Let's put this code in here, if MS is amenable. I would appreciate if you would push your testing strategy.

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This checklist is used to make sure that common guidelines for a pull request are followed.

Description of the change

Adds dask shim to ADLFS
.
This allows parallel access to Azure across a dask cluster of workers,
giving access to commands like

import dask.dataframe as dd
df = dd.read_parquet('adl://mybucket/path/to/data.parquet')

General Guidelines

• The PR has modified HISTORY.rst with an appropriate description of the change and a version increment.
• The PR has supporting test coverage that confirm the expected behavior and protects against regressions, including necessary recordings.
• Links to associated bugs, if any, are in the description.

[msftclas]

All CLA requirements met.

[coveralls]

Coverage decreased (-3.3%) to 80.956% when pulling 2d033da on martindurant:dasky into d18e47d on Azure:master.

[martindurant]

This PR is stale, closing now.
It would be far better at this point to refactor ADLFS to depend on fsspec for conformance with other filesystems and compliance with pyarrow, Intake and dask.