Add Karma Test Runner

* update package.json w/ karma dependencies
* add npm test script
* add node_modules to .gitignore

karma.conf.js

@@ -0,0 +1,42 @@
+'use strict';
+
+module.exports = function (config) {
+    config.set({
+
+        // base path, that will be used to resolve files and exclude
+        basePath: 'src',
+
+        // frameworks to use
+        frameworks: ['jasmine'],
+
+        // list of files / patterns to load in the browser
+        files: [
+            'Layout.js',
+            'Layout-test-utils.js',
+            '__tests__/Layout-test.js',
+            '__tests__/Layout-consts-test.js'
+        ],
+
+        plugins: [
+            'karma-chrome-launcher',
+            'karma-jasmine'
+        ],
+
+        // web server port
+        port: 9876,
+
+        // enable / disable colors in the output (reporters and logs)
+        colors: true,
+
+        // level of logging
+        // possible values: config.LOG_DISABLE || config.LOG_ERROR || config.LOG_WARN || config.LOG_INFO || config.LOG_DEBUG
+        logLevel: config.LOG_INFO,
+
+        browsers: ['Chrome'],
+
+        // If browser does not capture in given timeout [ms], kill it
+        captureTimeout: 60000,
+
+        singleRun: false
+    });
+};