Getdist

Misc fixes and updates

* Uses fast numpy loadtxt to load chains in numpy >= 1.23 (much faster than previous pandas fallback)
* Minor fixes

* GetDist GUI supports PySide 6
* Minor fixes

* Added [plot_4d](https://getdist.readthedocs.io/en/latest/plots.html#getdist.plots.GetDistPlotter.plot_4d) for 3-D colored scatter plots, with optional animation and mp4 export
* GUI updates for dark mode and dpi compatibility; copy image to clipboard
* Use numpy 1.17 Generators for random sampling
* MCSamples instances can now access parameter sample values via samples['name']
* Fixes for [Cobaya](https://cobaya.readthedocs.io/) chain load
* Bug fixes and updates for compatibility

Various small bug and version compatibility fixes.

- Support for plotting and gui loading chains from any hierarchy of folders given the root folder name as chain_dir
- Large speed up for analysing very long highly correlated chains (in getEffectiveSamplesGaussianKDE)
- Removed Python 2 support, updates for Python 3 (see Python2latest for Py2-compatible version)
- Fixes and updates for Cobaya chain compatibility including propagating fixed parameter values
- Removed paramgrid module (loaded from cosmomc if that is installed and configured)