Clean density calculation (#97)

* Get rid of utils

* Clean up imports

* Move some utils here

* Rename file

* Add simname to boxsize

* Add imports

* Delete old files

* Update README

* Update imports

* Add a new draft of the density calculator

* Update fields

* Draft of new density field calculatiosn

* Add snapshot

* Add boxsizes

* Little updates

* Bring back utils

* Edit docstrings

* Edits imports

* Add progress on snapshots

* edit improts

* add basic snapshot catalogue

* Add support for CSiBORG2 snapshot reader

* add paths to fofcat for csiborg2

* Add more imports

* Add more boxsize

* Add more imports

* Add field readers

* Simplify field paths

* Fix typo

* Add observer vp

* Clean up density field calculation

* Add a short note

* Edit args

* Remove old comments

* Edit docs

* Remove blank line

* Stop flipping RAMSES

* Remove comment

* Edit desc

* Remove normalization

* Remove old dist array

* Remove non-volume weighting

* Remove non-volume weight

* Add ignore of flake8 notebooks

* Fix path typo

* Fix units

* Edit paths docs

* Update nb

README.md

@@ -10,6 +10,8 @@ however with little effort it can support other simulations as well.
 ## TODO
 - [x] Prune old CSiBORG1 merger tree things.
 - [x] Add visualiastion of the density field.
+- [ ] Clear out `density` support.
+- [ ] Add sorting of Gadget4 initial snapshot like final snapshot.
 - [ ] Add full support for CSiBORG2 suite of simulations.
 - [ ] Add SPH field calculation from cosmotools.