cell response raster plots should show all neurons in the network model

[jasmainak]

trafficstars

As discussed in the group meeting, we should show all neurons, not just the neurons that spike.

[jasmainak]

Also we should use: https://matplotlib.org/3.1.1/api/_as_gen/matplotlib.pyplot.eventplot.html instead of scatter as mentioned by @ntolley

[samadpls]

@jasmainak, Can I take this issue, and Could you provide me with more context regarding this issue?

[jasmainak]

it's related to this function: https://jonescompneurolab.github.io/hnn-core/stable/generated/hnn_core.CellResponse.html#hnn_core.CellResponse.plot_spikes_raster

when some cells do not spike, this plot omits those cell types. Instead, we want to always plot every cell type.