Add shapes for callouts

[lindsayplatt]

Use a similar technique to how we get the water mark - create a png and then add the image at a specific location. See comments in #31 for more detail.

[lindsayplatt]

Still to do:

1. smooth out the polygon borders
2. eliminate overlaps between polygon and text and legend
3. move the legend to the bottom left while we're messing with component placement?
4. switch polygon color to something gentler, maybe one of the grays in the timeline clock

[lindsayplatt]

For 3, that might be tricky because of Alaska's tail, but we could do it if we added a bit more room between the edge of the map and the edge of the figure

[lindsayplatt]

For today, we will try to do 1 smooth out the polygon borders and 2 eliminate overlaps between polygon and text and legend.

[aappling-usgs]

Alison will do 2 by moving the california callout text

[mwernimont]

mwernimont did # 1 and # 4, unloaded images in slack channel

[lindsayplatt]

They have been added! Additional adjustments are captured in #78.