Replace closure compiler plugin with official one

Replace webpack-closure-compiler (deprecated) with closure-webpack-plugin,
which is official closure plugin.
Also, reworked CI.

package.json

@@ -11,9 +11,11 @@
   },
   "devDependencies": {
     "clean-webpack-plugin": "^3.0.0",
+    "closure-webpack-plugin": "^2.0.1",
     "copy-webpack-plugin": "^5.0.4",
     "coveralls": "^3.0.6",
     "del": "^5.0.0",
+    "google-closure-compiler": "^20190819.0.0",
     "gulp": "^4.0.2",
     "gulp-istanbul": "^1.1.3",
     "gulp-sourcemaps": "^2.6.4",
@@ -34,7 +36,6 @@
     "typescript": "^3.5.3",
     "webpack": "^4.39.2",
     "webpack-cli": "^3.3.6",
-    "webpack-closure-compiler": "^2.1.6",
     "webpack-dev-server": "^3.1.3"
   },
   "scripts": {
@@ -43,6 +44,8 @@
     "cover": "gulp coverage",
     "clean": "gulp clean",
     "all": "gulp default",
+    "build-prod": "gulp build_prod",
+    "build-stage": "gulp build_stage",
     "browser-test": "karma start",
     "webpack": "webpack",
     "dev-server": "webpack-dev-server"