addBreakColorLegend: Adds a Legend to sp Plots with Colors and Breaks
In jayverhoef/POP: Platform of Opportunity Data and Models

Adds a Legend to sp Plots with Colors and Breaks

addBreakColorLegend(
  xleft,
  ybottom,
  xright,
  ytop,
  breaks,
  colors,
  printFormat = "4.2",
  ...
)

`xleft`	a scalar of the left x position.
`ybottom`	a scalar of bottom y position.
`xright`	a scalar of the right x position.
`ytop`	a scalar of top y position.
`colors`	a vector of colors, should have one less element than the number of breaks.
`brks`	the breaks between color classes. Needs a lower bound, and upper bound, so there should be one more break than number of classes.
`printFormat:`	a character variable in '4.2' format where the 4 control the number of digits before the decimal, and 2 controls the number of digits after the decimal.