Build: Migrate from JSHint to ESLint

Closes gh-577

Author: mgol

.jshintignore renamed to .eslintignore

@@ -1,3 +1,5 @@
 external/**
 jquery-ui/**
+template/**
 tmp/**
+*.min.js

.eslintrc.json

@@ -0,0 +1,25 @@
+{
+  "root": true,
+
+  "extends": "jquery",
+
+  "reportUnusedDisableDirectives": true,
+
+  "parserOptions": {
+    "ecmaVersion": 2018
+  },
+
+  "env": {
+    "es6": true,
+    "node": true
+  },
+
+  "rules": {
+    "strict": [ "error", "global" ],
+
+    // Too many violations
+    "camelcase": "off",
+    "max-len": "off",
+    "no-unused-vars": "off"
+  }
+}