Add basic e2e test

Running nightwatch tests requires that the latest selenium webdriver JAR
be present at `:project_root:/bin/selenium-server-standaline.jar`. See the
nightwatch [Getting started](http://nightwatchjs.org/guide#installation) page for more information.

Use `npm run e2e` to run the end to end tests.

.gitignore

@@ -1,4 +1,8 @@
 test-bundle.js
 .DS_Store
 node_modules
-example/bundle.js
+example/bundle.js
+# Process management from the foreman ruby gem.
+Procfile
+bin/*.jar
+__tests__/reports

__tests__/e2e/appTest.js

@@ -0,0 +1,10 @@
+module.exports = {
+  'Test content length': function(browser) {
+    browser
+      .url('http://localhost:5100')
+      .waitForElementVisible('body', 1000)
+      .setValue('.ContentEditable', 'this is some text')
+      .assert.containsText('#content-length', '126')
+      .end()
+  }
+};