LFP forward model scripts etc.

[espenhgn]

Base setup for LFP predictions. Not yet incorporated into main workflow files.

Closes #3 in due time

[espenhgn]

Ok @jhnnsnk ; I think we can call this v0.1 of the LFP simulation setup avaiting the TC population(s). The corresponding workflow should be in place so that a bash script (lfp.sh) is created and can optionally be run. It's only implemented and tested for the mesocircuit model, and I don't see a reason to incorporate it for the microcircuit cases (maybe it will work out of the box - unlikely - but who knows) as we don't have that planned for the manuscript.

The main sim script is run_lfp_simulation.py, while auxiliary files are in core/lfp/. Parameters are derived from those in net_dict and sim_dict.

[espenhgn]

@jhnnsnk, this all seems to work as I intended now.

Closes #43, #27 on top of #3

[jhnnsnk]

Thanks for the integration!