Update basic analysis tutorial - more figure explanation, add cell type analysis

[dlevenstein]

• update the basic analysis docs (https://prnn.readthedocs.io/en/latest/basic_analysis.html) with further explanations of the figures based on your new understanding? The idea would be to put in images of the figures (similar to how they're in quickstart), and walk through each panel. That way whoever goes through them next has a better explanation of what everything is
• add cell type analysis to basic analysis docs
• more offline trajectories to new tutorial about sleep/replay analysis