Add make commands for building css from sass via webpack

Author: podliashanyk

Makefile

@@ -1,4 +1,4 @@
-.PHONY: dummy clean distclean testclean docclean doc .FORCE
+.PHONY: dummy clean distclean testclean docclean doc cssclean sassbuild sasswatch .FORCE
 
 dummy:
 	@echo "'make' is no longer used for deployment. See 'doc/intro/install.rst'"
@@ -32,4 +32,17 @@ doc/reference/alerttypes.rst: .FORCE
 	echo "UID=$(shell id -u)" >> .env
 	echo "GID=$(shell id -g)" >> .env
 
+cssclean:
+	-rm -rf python/nav/web/static/css
+
+sassbuild: cssclean
+	@if [ -f package-lock.json ]; then \
+		(npm ci && npm run build:sass); \
+	else \
+		(npm install && npm run build:sass); \
+	fi
+
+sasswatch:
+	-npm run watch:sass
+
 .FORCE: