Create How-to and Explanation guides for statistical plots

[Azaya89]

closes #1664

This PR creates 2 new How-to guides for visualizing multivariate and time series plots as well as explanation guides for understanding hvPlot's statistical plot types. The PR does not directly use the content from the Statistical Plots User Guide notebook but draws heavy inspiration from, and expands on, it.

• Create How-To guide on visualizing Multivariate Data
• Create how to guide on analyzing Time Series data with Lag Plots
• Add Explanation guide to understanding hvPlot's Statistical Plot types.

[maximlt]

• Add direct links to the reference pages
• Add plot illustrations (with code or image) to the explanation page
• The data for parallel coordinates and Andrews curves have to be normalized before plotting (see their reference)
• Remove the lag plot how-to (we might add later a how-to for time series data)
• Decide whether you want an explanation AND a how-to for statistical plots
• Explanation: add more plots (bivariate, heatmap, density, ...)
• Explanation: Sort the sections (e.g. distribution, multivariate, time series)
• Read https://seaborn.pydata.org/tutorial/relational.html and https://seaborn.pydata.org/tutorial/distributions.html for inspiration

[Azaya89]

• Add direct links to the reference pages

Done

• Add plot illustrations (with code or image) to the explanation page

Done

• The data for parallel coordinates and Andrews curves have to be normalized before plotting (see their reference)

Done

• Remove the lag plot how-to (we might add later a how-to for time series data)

Removed the How-to notebook entirely

• Decide whether you want an explanation AND a how-to for statistical plots

Decided

• Explanation: add more plots (bivariate, heatmap, density, ...)

Done

• Explanation: Sort the sections (e.g. distribution, multivariate, time series)

Done

• Read https://seaborn.pydata.org/tutorial/relational.html and https://seaborn.pydata.org/tutorial/distributions.html for inspiration

• Read