Issue #2227731 by _nod: Replace JSHint with ESLint for JavaScript validation.

.jshintignore → .eslintignore

-core/assets/vendor
+core/assets/vendor/*
+core/modules/locale/tests/locale_test.js
 core/modules/tour/js/jquery.joyride-2.0.3.js
-core/vendor
+core/vendor/*
 sites/*/files

.eslintrc

+{
+  "env": {
+    "browser": true
+  },
+  "globals": {
+    "Drupal": true,
+    "drupalSettings": true,
+    "domready": true,
+    "jQuery": true,
+    "_": true,
+    "matchMedia": true,
+    "Backbone": true,
+    "Modernizr": true,
+    "CKEDITOR": true
+  },
+  "rules": {
+    "eqeqeq": [2, "smart"],
+    "guard-for-in": 2,
+    "no-undef": 2,
+    //"no-unused-vars": [2, {"vars": "local", "args": "none"}],
+    "no-unused-vars": 0,
+    "strict": 2,
+    "new-cap": 0,
+    "quotes": 0,
+    "camelcase": 0,
+    "no-underscore-dangle": 0,
+    "no-new": 0,
+    "no-alert": 0,
+    "no-use-before-define": 0,
+    "consistent-return": 0,
+    "no-constant-condition": 0
+  }
+}

.jshintrc

-{
-  "browser"   : true,
-  "curly"     : true,
-  "eqeqeq"    : true,
-  "forin"     : true,
-  "indent"    : 2,
-  "latedef"   : true,
-  "newcap"    : true,
-  "noarg"     : true,
-  "strict"    : true,
-  "trailing"  : true,
-  "undef"     : true,
-  "unused"    : "vars",
-  "predef"    : [
-    "Drupal",
-    "drupalSettings",
-    "domready",
-    "jQuery",
-    "_",
-    "matchMedia",
-    "Backbone",
-    "Modernizr",
-    "CKEDITOR"
-  ]
-}