Make image packaging and installation optional

Eventually, images should not be transferred as part of the application package,
using a more efficient mechanism instead. Other cases may already exist where
packaging without the image is preferrable.

When the `PACKAGE_IMAGES` variable is not set to 1 (default: 1), images will not
be included in the package. The installation script now handles the case where
the `images` folder is missing altogether.

install.sh

@@ -37,7 +37,7 @@ echo "importing root files"
 cp -rfv $LOCATION/root/* /
 
 # import docker images
-for f in $(find $LOCATION/images -name "*.img");do
+for f in $(find $LOCATION/images -name "*.img" 2>/dev/null);do
   echo "importing docker image: $f"
   docker load -i $f
 done