Create Figure Richness & Figure Hotspots script

[jcoliver]

Overlap in data processing steps warrants combination of richness maps and hotspots maps into a single script.

Old location & names:

• src/summary/create-manuscript-objects.R
• src/summary/create-supplement-objects.R

New location & name: src/manuscript/fig-3-richness.R

• Richness: Five panel figure showing (a) contemporary species richness, (b) contemporary richness hotspots (>= 4 species), (c) forecast richness for SSP3-7.0, 2050s, (d) forecast richness hotspots, and (e) the difference in richness between (a) and (c)
• Supplemental Richness: Six panel figure of species richness estimates of all combinations of forecast SSP / time points
• Supplemental Hotspots: Six panel figure of richness hotspots for all combinations of forecast SSP / time points