Migration needed from googlesheets to googlesheets4

[florisvdh]

Needed because Google will drop its Sheets API v3 and googlesheets functionality is suffering already.

Beside code migration to googlesheets4, a convenient way must be implemented for avoiding google authentication when reading publicly readable googlesheets - which is the case for the googlesheets used here. This page will be a good guide. I think sheets_deauth() will be the way to go as we (should) only work with public googlesheets in these repositories.

For examples of various current errors and warnings, see PR #36.

[florisvdh]

From the following grep-output you can see in which projects googlesheets is loaded:

./src/generate_habitatmap_stdized/index.Rmd:49:library(googlesheets)
./src/generate_habitatmap_terr/index.Rmd:49:library(googlesheets)
./src/generate_habitatsprings_updates/index.Rmd:44:library(googlesheets)
./src/generate_watersurfaces_hab/index.Rmd:48:library(googlesheets)