Use BOX_ENV instead of NODE_ENV

Let NODE_ENV be used by node modules and always be set to production

Fixes #453

src/scripts/rmappdir.sh

@@ -17,7 +17,7 @@ if [[ "$1" == "--check" ]]; then
     exit 0
 fi
 
-if [[ "${NODE_ENV}" == "cloudron" ]]; then
+if [[ "${BOX_ENV}" == "cloudron" ]]; then
     readonly app_data_dir="${HOME}/data/$1"
     if [[ -d "${app_data_dir}" ]]; then
         find "${app_data_dir}" -mindepth 1 -delete