Add Python bindings to Brew formula

[aWZHY0yQH81uOYvH]

Fixes https://github.com/thliebig/openEMS/issues/135 and fixes https://github.com/thliebig/CSXCAD/issues/38.

Python bindings are now installed by default (but can be disabled) when installing with Homebrew.

Currently a draft PR because

• Is this really the best way to install Python libraries? I really don't like the hard-coded versions, but that seems to be suggested by their guide and it makes installing matplotlib extremely complicated because of all its dependencies. Pending discussion here. An alternative would be to have the end user install packages with pip themselves but that seems counterproductive.
• Should matplotlib be installed? Currently only cython (from bottle), numpy (from bottle), and h5py (from source) are installed. Those are the only required libraries for the bindings to work, but matplotlib is used in tutorials. It looks like matplotlib would need to be installed from source, which would make the install take forever and would significantly complicate things.
• Given the fixed version of the packages, should a Python 3 sub-version be pinned (like 3.12) instead of just specifying the latest Python 3?
• When uninstalled via brew, openEMS and CSXCAD remain as weird ghost empty packages that can be imported but don't contain anything.

[aWZHY0yQH81uOYvH]

I think this is ready now. There is now a matplotlib bottle, and I decided to just use pip to install the latest version of h5py instead of pulling some specific version since that sounds annoying to maintain.

Also the "ghost package" thing I mentioned was just some empty directories with __pycache__ stuff in them. Not a big deal.

[aWZHY0yQH81uOYvH]

Also @thliebig ping on this one if you haven't seen it recently. I fixed it up yesterday.