add luacheck and integration test workflows / fix luacheck errors

partially attends to https://github.com/pandorabox-io/pandorabox.io/issues/444 (the ObjectRef issue)

integration-test.sh

@@ -0,0 +1,20 @@
+#!/bin/sh
+# simple integration test
+
+CFG=/tmp/minetest.conf
+MTDIR=/tmp/mt
+WORLDDIR=${MTDIR}/worlds/world
+
+cat <<EOF > ${CFG}
+ enable_3d_armor_integration_test = true
+EOF
+
+mkdir -p ${WORLDDIR}
+chmod 777 ${MTDIR} -R
+docker run --rm -i \
+	-v ${CFG}:/etc/minetest/minetest.conf:ro \
+	-v ${MTDIR}:/var/lib/minetest/.minetest \
+	-v $(pwd):/var/lib/minetest/.minetest/worlds/world/worldmods/3d_armor \
+	registry.gitlab.com/minetest/minetest/server:5.0.1
+
+test -f ${WORLDDIR}/integration_test.json && exit 0 || exit 1