Experiment with interfacing with Dask

Look into the different submodules whether there are blocking issues for adding support for Dask.

cc @Cadair @astrofrog @eteq

Start by reviewing Astropy’s submodules and the current Dask interfaces or requirements to identify where support could be blocked. Record the affected submodules, the specific blocking issues, and whether any clear path exists for adding Dask support; the issue does not name particular files or tests.

Written by the indexing model from the issue text.