leaflet map improvements

[stevenpbachman]

• add legends to maps to show native range, GBIF points etc.
• dynamic control of map elements e.g. native range clip - use leafletProxy - https://rstudio.github.io/leaflet/shiny.html

[stevenpbachman]

https://stackoverflow.com/questions/52819951/how-do-i-click-on-a-leaflet-map-create-a-marker-and-then-delete-that-marker-wh

[stevenpbachman]

This could be useful: https://cran.r-project.org/web/packages/leaflet.extras/leaflet.extras.pdf

[stevenpbachman]

https://stackoverflow.com/questions/34348737/r-leaflet-how-to-click-on-map-and-add-a-circle