make: add independent statik-only goal

To separate the asset to golang conversion step from the node app build,
we add a new, independent goal for just the statik command. That way we
can cleanly separate between stuff that needs yarn/nodejs installed and
stuff that needs golang installed.

Author: guggero

Makefile

@@ -97,10 +97,12 @@ yarn-install:
 # ============
 # INSTALLATION
 # ============
-statik-build: $(STATIK_BIN) app-build
+statik-only: $(STATIK_BIN)
 	@$(call print, "Building statik package.")
 	statik -src=app/build
 
+statik-build: app-build statik-only
+
 build: statik-build go-build
 install: statik-build go-install