refactor(config.js): Extract config file

* Separate different config source to each files
* Freeze config object

package.json

@@ -28,6 +28,7 @@
     "connect-session-sequelize": "^4.1.0",
     "cookie": "0.3.1",
     "cookie-parser": "1.4.3",
+    "deep-freeze": "^0.0.1",
     "diff-match-patch": "git+https://github.com/hackmdio/diff-match-patch.git",
     "ejs": "^2.5.5",
     "emojify.js": "~1.1.0",
@@ -162,8 +163,8 @@
     "less-loader": "^2.2.3",
     "optimize-css-assets-webpack-plugin": "^1.3.0",
     "script-loader": "^0.7.0",
-    "style-loader": "^0.13.1",
     "standard": "^9.0.1",
+    "style-loader": "^0.13.1",
     "url-loader": "^0.5.7",
     "webpack": "^1.14.0",
     "webpack-parallel-uglify-plugin": "^0.2.0"