Configure ESLint in all directories with JS code

Next commits will use this configuration to lint the codebase.

.eslintrc

+{
+  // This file contains root configuration for ESLint. Its rules may be overriden in a specific
+  // folder (e.g., tests) by placing .eslintrc in it. 
+  // All lint rules should be placed here unless they do not apply to entire JavaScript codebase.
+  // For example, indentation rules should be here (applies to all JS files), but Protractor
+  // should not (applies only to integration tests files).
+
+  // Base rules on recommended ESLint settings.
+  // TODO(bryk): Determine whether there is a better base config.
+  "extends": "eslint:recommended",
+  "env": {
+    // Enables all ES6 features except modules.
+    "es6": true
+  },
+  "ecmaFeatures": {
+    // Enable ES6 modules to have all language features covered.
+    "modules": true
+  }
+}

build/.eslintrc

+{
+  "env": {
+    // Build files are written in node.
+    "node": true
+  }
+}
\ No newline at end of file

src/app/frontend/.eslintrc

+{
+  // Load eslint-plugin-angular to have angular specific checks.
+  "plugins": ["angular"],
+  "rules": {
+    // Disable undefined variable checking. This is done by the compiler. 
+    "no-undef": 0
+  }
+}

src/test/frontend/.eslintrc

+{
+  "env": {
+    "jasmine": true,
+  }
+}

src/test/integration/.eslintrc

+{
+  "env": {
+    "jasmine": true,
+  	"protractor": true
+  }
+}

src/test/integration/main.po.js

@@ -23,5 +23,4 @@ export class MainPage {
     this.jumbEl = element(by.css('.jumbotron'));
     this.h1El = this.jumbEl.element(by.css('h1'));
   }
-};
-
+}