Add short names and clean up posterior descriptions

[avehtari]

When using many posteriors in a paper it would be useful to have short names that can be used in plots, like in this example

And then include a table listing the unique long posterior name, the short name in plot, and a description as in this example

Currently, the database does not include such short names. Furthermore, currently the description use quite different word orders, varying capitalization, and varying information. It would be good to look at the all descriptions together and make them look more similar in style, as I did manually for the above table example. (I also had to compile all the models and instantiate the posteriors to get the correct posterior dimensions, see #294).

With the improvements in the short names, dimension count, and short description we could then add code examples to show how to easily make a table similar to above example to be added in paper appendix. For example, I created a dataframe with the desired information and then in R

library(tinytable)
pdbnames |> tt() |> print("latex")

and then a few adjustments for the latex code to make it span two pages in PDF.

[MansMeg]

This is a very good idea! Lets put this in the backlogg @JTorgander .