adds LFPy@2.2.3

This PR adds the LFPy Python package.

merged

mentioned in commit e0d0f6b2

Hi @ehagen Thanks for contributing.

I made one correction to your Spack package here.
Unfortunately it fails because of a dependency that is missing:
==> Error: Package 'py-lfpykit' not found in repository '/srv/test-build/ebrains-spack-builds'
You need to create a Spack package also for 'py-lfpykit'

Thanks, @akarmas. I had more or less forgotten about this. I'll try and add LFPykit (and its dependencies) in another PR. I'll update LFPy to v2.2.6 at the same time.

mentioned in issue #11 (closed)