Collected issues from Hackathon

* [x] Rename parameter `V` to `NVARS`
* [x] In `Tree`, rename parameter `D` to `NDIMS` for consistency
* [x] Should we rename `N` to something like `NPOLYDEG`?
* [x] Clean up parameter files (e.g., move `ndims = x` to its proper place, delete commented lines)
* [ ] Rewrite `get_name` to return name without `2D`/`3D` for equations and DG
* [ ] `interpolation.jl`: clean up and/or split up (move to `utils/` folder?)
* [x] Rename `riemann!` (it seems to be only used for EC mortar and non-conservative terms)
* [ ] Update README for parameter files
* [ ] Improve `calc_dt` for Euler + LSA to make them work in 2D and 3D with the same CFL number
* [ ] ASCII art: add visual documentation in comments for 3D connectivity and element numbering for mortars
* [x] `prolong2mortars`: Simplify code
* [ ] Add proper AMR tests for 3D
* [ ] Add properly implemented periodic pulse for LSA (with modulo?)
* [ ] optimize shock capturing setup for Sedov blast and self-gravity Sedov blast
* [x] remove obsolete AMR indicators in 3D

This is a broad checklist with several completed and open items; start by confirming which unchecked task is still wanted. For the named work, read interpolation.jl and the README parameter-file documentation, and inspect the existing calc_dt, get_name, and AMR test entry points. Done means one clearly scoped item is completed with its relevant tests or documentation updated.

Written by the indexing model from the issue text.