Create list of package versions

[bdevans]

In response to the discussion about synchronising package versions across the whole project (#1449 (comment)), as an interim measure, this is a manually curated list of files which contain package versions, enabling us to check them and update as necessary when updating a dependency.

[bdevans]

I may have missed some and it might be better to tidy it away in the dev folder, but it's a start!

[mstimberg]

Oh, thanks a lot, that's really useful. It also clearly shows what a mess everything is 😬
And it reminded me that we should get rid of the conda recipe, the actual recipe we use is https://github.com/conda-forge/brian2-feedstock/blob/main/recipe/meta.yaml

I may have missed some and it might be better to tidy it away in the dev folder, but it's a start!

The words "tidy" and "dev folder" don't quite work together in our repo ;-)