New function PlotRobinson() development

Hi @nperez @nmilders @erifarov

I open this issue to track the remaining issues in PlotRobinson(). We don't need to check all the boxes but it's good to have a record.

• Complete documentation
• When parameter legend is ggplot2: Check if include.lowest parameter from cut() can include all the lower values. Check s2dv!146 (closed) for more explanation
• Parameter vertical: to make the horizonal colorbar looks nicer
• Check if other projection works (e.g., Arctic area: 3995)
• Check if layout() works better than cowplot
• Can cowplot show legend in pop-up window? Change p to p_legend in the last line
• Rename the function from PlotRobinsonMap() to PlotRobinson()
• Check if plotting a region works https://earth.bsc.es/gitlab/es/s2dv/-/merge_requests/146#note_210535
• Use it with PlotLayout()
• If there is a way to plot polygons instead of dots? For now, the plotting is dots, so if the dot size is not appropriate, they overlap or the plot has too much white space. The difficulty lies in transforming to different projection. The polygons can be generated correctly with regular grids.
• Global polygon

Let me know if I miss anything. I'll report my progress here.

Function: https://earth.bsc.es/gitlab/es/s2dv/-/blob/develop-PlotRobinson/R/PlotRobinson.R

Best,
An-Chi