PLT-5755: Infrastructure for Component Testing. (#5814)

This migrates the existing webapp tests to using Jest and Enzyme. The
infrastructure is put in place for React component testing, and a few
simple example component tests are implemented.

This also adds snapshot testing of components, coverage checking for the
webapp (although that is not yet integrated to Coveralls), and the
ability to run npm run test:watch to automatically re-run affected tests
when working on the webapp codebase.

Makefile

@@ -1,4 +1,4 @@
-.PHONY: build package run stop run-client run-server stop-client stop-server restart restart-server restart-client start-docker clean-dist clean nuke check-style check-client-style check-server-style check-unit-tests test dist setup-mac prepare-enteprise run-client-tests setup-run-client-tests cleanup-run-client-tests test-client build-linux build-osx build-windows internal-test-client vet
+.PHONY: build package run stop run-client run-server stop-client stop-server restart restart-server restart-client start-docker clean-dist clean nuke check-style check-client-style check-server-style check-unit-tests test dist setup-mac prepare-enteprise run-client-tests setup-run-client-tests cleanup-run-client-tests test-client build-linux build-osx build-windows internal-test-web-client vet run-server-for-web-client-tests
 
 # For golang 1.5.x compatibility (remove when we don't want to support it anymore)
 export GO15VENDOREXPERIMENT=1
@@ -254,6 +254,9 @@ test-server: test-te test-ee
 internal-test-web-client: start-docker prepare-enterprise
 	$(GO) run $(GOFLAGS) ./cmd/platform/*go test web_client_tests
 
+run-server-for-web-client-tests:
+	$(GO) run $(GOFLAGS) ./cmd/platform/*go test web_client_tests_server
+
 test-client: start-docker prepare-enterprise
 	@echo Running client tests