Better module checking/initializing mechanism

1. Print a message to tell if modules need to be initialized when running `make serve` or other similar targets, and stop current make procedure.
2. Provide `module-init` target to initialize all dependencies

Co-authored-by: Tim Bannister <tim@scalefactory.com>

Makefile

@@ -19,7 +19,11 @@ help: ## Show this help.
 	@awk 'BEGIN {FS = ":.*?## "} /^[a-zA-Z_-]+:.*?## / {sub("\\\\n",sprintf("\n%22c"," "), $$2);printf "\033[36m%-20s\033[0m %s\n", $$1, $$2}' $(MAKEFILE_LIST)
 
 module-check:
-	@git submodule status --recursive | awk '/^[+-]/ {printf "\033[31mWARNING\033[0m Submodule not initialized: \033[34m%s\033[0m\n",$$2}' 1>&2
+	@git submodule status --recursive | awk '/^[+-]/ {err = 1; printf "\033[31mWARNING\033[0m Submodule not initialized: \033[34m%s\033[0m\n",$$2} END { if (err != 0) print "You need to run \033[32mmake module-init\033[0m to initialize missing modules first"; exit err }' 1>&2
+
+module-init:
+	@echo "Initializing submodules..." 1>&2
+	@git submodule update --init --recursive --depth 1
 
 all: build ## Build site with production settings and put deliverables in ./public