Move to a modern testing infrastructure

Use Jest as test framework, and restructured ESLint config files so it applies to each directory separately.

.eslintrc.js

@@ -0,0 +1,30 @@
+module.exports = {
+  'env': {
+    'browser': false,
+    'es6': true,
+    'node': true
+  },
+  'extends': [
+    'eslint:recommended',
+    'plugin:node/recommended',
+    'standard'
+  ],
+  'plugins': [
+    'node'
+  ],
+  'rules': {
+    // Override some of standard js rules
+    'semi': [ 'error', 'always' ],
+    'comma-dangle': [ 'error', 'only-multiline' ],
+    'camelcase': 'off',
+    'no-var': 'error',
+    'prefer-const': 'error',
+    'arrow-parens': [ 'error', 'as-needed' ],
+    'standard/array-bracket-even-spacing': 'off',
+    'array-bracket-spacing': [ 'error', 'always', { 'objectsInArrays': false }],
+    'object-curly-spacing': [ 'error', 'always' ],
+
+    // Override some eslint base rules because we're using node.
+    'no-console': 'off',
+  }
+};

api/hosts-api.js

@@ -271,7 +271,7 @@ credentialsAPI.delete({
       return;
     }
 
-    hosts.resetOAuth2ClientSecret(host, (error) => {
+    hosts.resetOAuth2ClientSecret(host, error => {
       if (error) {
         response.statusCode = 500; // Internal Server Error
         response.json({ error: 'Could not reset host credentials' }, null, 2);