Updates to multichannel timeseries

[droumis]

• Add simple hvPlot version
• Make the thumbnail image match the other neuroscience thumbnails. Remove the cartoon from the actual app and just use thumbnail image
• Add extension demonstrating use of multiple data type groups with different time sampling (e.g. Position)
• Add complete copy-pastable app code block at the end (or a link to a .py file of it in the examples repo)