Use a more efficient mechanism for passing data and subsets to OpenSpace

[astrofrog]

This requires changes in OpenSpace, but tables with ~10^5-6 rows or more, it's going to be critical to have the ability to pass the data to OpenSpace in binary form, either using a binary file format, or by somehow sharing memory. The former is probably easier, and will be required anyway if OpenSpace is running on a separate machine from glue.

For subsets, the ideal solution would be to be able to tell OpenSpace that a data layer is a subset of another layer, and provide a bit/boolean mask array indicating which elements to pick.

[astrofrog]

Somewhat related, we should update this plugin to use OpenSpace/OpenSpace#910