Firefly

- Lots of bug fixes related to working on the flask server, and particularly when splitting the gui and viewer
- Added an initial implementation of data selection (within a sphere) and accessing that data within Python or via download. This includes a new component to the GUI to enable the data selection. NOTE: this has not been tested with octree data sets.
- Added the ability to set and get settings from Python

Replaces `pandas` json loading with `json` so we don't continue to break [yt](https://github.com/yt-project/yt)'s CI. Thanks neutrinoceros !

Pinging ageller just in case.

Minor update to the citation information

What's Changed
* Docs fix by agurvich in https://github.com/ageller/Firefly/pull/173


**Full Changelog**: https://github.com/ageller/Firefly/compare/v3.2.1...v3.2.2

Loop over default settings using `defaultSettings.json` and `defaultParticleSettings.json`, among other changes.

massive changes, biggest ones:

1. replacement of JSONs with .ffly binary format (much smaller and much faster to read!)
2. ability to optionally format binary data into .fftree, indexed by an octree.json file allowing the app to progressively render only what is on screen
3. super slick new UI (all credit to ageller !!)
4. longstanding bug fixes
5. the ability to scale radius by any field
6. official support for the column density rendering mode
7. updated the default dataset to reflect the all the new features! (it's big though, 73 Mb so don't use mobile data...)

And probably more.