Small EDA page updates

[lukestein]

• Removed use of deprecated set_precision formatter (note the replacement format() can also handle the display of nans rather than changing the cell contents using fillna(), but I didn't make this code change
• Suggested transposition of summary stats tables
• Mention pivot_table as alternate way of formatting data
• A bit more on background_gradient
• Minor changes

[lukestein]

btw I need to include %matplotlib inline to get the graphs to render in these notebooks, but didn't add it since I don't know how it interacts with the book generation process

[aeturrell]

This all looks fantastic. Made a couple of minor changes related to dataprep.