Chore: Add ESLint (javascript code linter)

.eslintrc

@@ -0,0 +1,8 @@
+{
+    "extends": "eslint:recommended",
+    "env": {
+        "browser": true
+    },
+    "rules": {
+    }
+}

cypress/.eslintrc

@@ -0,0 +1,11 @@
+{
+    "env": {
+        "es6": true,
+        "mocha": true
+    },
+    globals: {
+        "Cypress": true,
+        "cy": true,
+        "expect": true
+    },
+}

package.json

@@ -9,7 +9,8 @@
     "dev": "npm start -- -o",
     "test": "start-server-and-test start http://localhost:8080 test:cypress",
     "test:cypress": "cypress run",
-    "test:watch": "npm start & cypress open"
+    "test:watch": "npm start & cypress open",
+    "lint": "eslint . *.js --ignore-pattern 'index.js'"
   },
   "repository": {
     "type": "git",
@@ -25,6 +26,7 @@
   "license": "MIT",
   "devDependencies": {
     "cypress": "^3.1.2",
+    "eslint": "^5.9.0",
     "http-server": "^0.11.1",
     "start-server-and-test": "^1.0.1"
   }