Add banner text to main.min.js (#880)

- Add `---` YAML Front Matter as a workaround to allow the theme gem's version to be overridden locally.
- Adjust page scope in Front Matter default to avoid adding a layout to `main.min.js`
- Fixes #874, Fixes #722

package.json

@@ -27,7 +27,8 @@
   },
   "scripts": {
     "uglify": "uglifyjs assets/js/vendor/jquery/jquery-1.12.4.min.js assets/js/plugins/jquery.fitvids.js assets/js/plugins/jquery.greedy-navigation.js assets/js/plugins/jquery.magnific-popup.js assets/js/plugins/jquery.smooth-scroll.min.js assets/js/_main.js -c -m -o assets/js/main.min.js",
+    "add-banner": "node banner.js",
     "watch:js": "onchange \"assets/js/**/*.js\" -e \"assets/js/main.min.js\" -- npm run build:js",
-    "build:js": "npm run uglify"
+    "build:js": "npm run uglify && npm run add-banner"
   }
 }