Fetch pkg/lib automatically from cockpit instead of keeping a local copy

* remove mustache module as it's not used anymore.
* port alert component to react-core as the current code creates a
broken UI

Makefile

@@ -12,6 +12,8 @@ VM_IMAGE=$(CURDIR)/test/images/$(TEST_OS)
 NODE_MODULES_TEST=package-lock.json
 # one example file in dist/ from webpack to check if that already ran
 WEBPACK_TEST=dist/index.html
+# one example file in src/lib to check if it was already checked out
+LIB_TEST=src/lib/cockpit-po-plugin.js
 
 all: $(WEBPACK_TEST)
 
@@ -160,6 +162,12 @@ test/common:
 	git checkout --force FETCH_HEAD -- test/common
 	git reset test/common
 
+# checkout Cockpit's PF/React/build library; again this has no API stability guarantee, so check out a stable tag
+$(LIB_TEST):
+	git clone -b 256 --depth=1 https://github.com/cockpit-project/cockpit.git tmp/cockpit
+	mv tmp/cockpit/pkg/lib src/
+	rm -rf tmp/cockpit
+
 $(NODE_MODULES_TEST): package.json
 	# if it exists already, npm install won't update it; force that so that we always get up-to-date packages
 	rm -f package-lock.json