Fix export image from map display after upgrade to R 4.2.1

[isomemo]

@arunge See error message concerning a missing package in the screenshot below

[arunge]

@isomemo Yes, this we have to fix because of the upgrade of the R-version as mentioned in:

• https://github.com/Pandora-IsoMemo/data-tools/issues/15#issuecomment-1441974766

[isomemo]

@arunge Ok

[jan-abel-inwt]

The export function of the leaflet map is re-enabled in the beta-app