resolve #80 and simplify aesthetic calculations for scatterplot. remo…

[pburnsdata]

resolve #80 and simplify aesthetic calculations for scatterplot. Remove toolbars from plotlys

Things I don't love:

• the magic math for placements
• the hardcoded cut offs (tho they follow specs)
• the intensity of the colors
• it's not square

But idk how much these all matter - we'll need roxygen in here too ultimately, perhaps even arguments. interested to hear what you think @elimillera