improve add_recessions

[matthewstern]

• Inherit min, max, and type (date vs int) of x axis from the primary aes, rather than specifying them again. (see ggproto, as implemented in geom_text_lastonly?)
• cut off rectangles at highest and lowest grid lines rather than plot y axis min and max (better solution may be to define the y axis min and max as highest and lowest gridline so ymin = first gridline and ymax = last gridline).
• not really an enhancement, but we'll need to confirm down the road that "recessions" text defaults to correct font and size once theme_cmap is applied.
• there may be a way to improve the text_nudge_x argument's default to work better in more instances. Will need to play around.

[matthewstern]

to do this I need to unpack a little bit more, and create an altered ggproto object for GeomRect that inherits data from the top-level command. See https://ggplot2-book.org/internals.html and Noel's work with last point highlighting.

[matthewstern]

ggproto for rectangles is established. This inherits primary dataframe and uses that to filter the recessions. I have not yet figured out how to inherit the type of data...I am not sure this is possible.

Next step is to use the same framework to build a ggproto for text. Should be relatively straightforward.

[matthewstern]

this is done. We may have to come back around to confirming fonts once theme_cmap is further along.