Update to work with LFPy2.2

The original version did not work with LFPy2.2, because of substantial changes in LFPy.
It has now been updated, and should be more future proof.

Version used for published fiugres

This is the version of the code used to generate the figures in:
Næss et al. (2021) Biophysically detailed forward modeling of the neural origin of EEG and MEG signals. Neuroimage 225:2020.07.01.181875.
https://pubmed.ncbi.nlm.nih.gov/33075556/

This code is not compatible with LFPy versions newer than 2.1