adding a plotly interactive timechop function

[mihirbhaskar]

• A more interactive, flexible timechop plot, possibly helpful for playing around with parameters and understanding them. The function is called visualize_chops_plotly
• Updated docs for this
• A new dependency of plotly

See a notebook with the function in action here

Some possible next steps on this:

1. Add more labels of all the things in the temporal config on the graph (e.g. label timespan parameter, test durations, etc.)
2. Improve figure sizing (adapted based on number of subplots chosen for display)
3. Adding total cohort/data size for train and validation

[KasunAmare]

Took a quick look at the code, and played with the colab version a little. This looks pretty good to me. For now, I'm merging this with the dev branch to further testing