Swap R base plots in tutorial w/ ggplot2

[hannesdatta]

Background:

• The tutorial on data exploration uses some legacy function to plot the data (in particular, R's plot function).

Deliverable:

• Change all of the plotting information in section 3 of the notebook to ggplot2
• The graphs need to be properly formatted and "look" professional, so make sure to use necessary (but minimal) styling (axes labels, titles, etc.)
• Please also include a brief description about ggplot2 and why it's good to use it (you may look around on the web for some insights)
• Contribute change as a PR.

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