removing Web UI tutorials, updating remaining 4 to current release, + review pass

src/site/docs/tutorials/get-started/index.markdown

 ---
 layout: default
 title: "Get Started"
 description: "Get Dart and run two Dart applications"
 has-permalinks: true
 tutorial:
   id: get-started
 js:
 - url: /js/os-switcher.js
   defer: true
 - url: /js/editor-downloads-analytics.js
   defer: true
 - url: /js/editor-version.js
   defer: true
 next: connect-dart-html/
 next-title: "Connect Dart & HTML"
 prev: 
-prev-title: "A Game of Darts"
+prev-title: "Home"
 ---
 
 {% capture whats_the_point %}
 
 * The Dart bundle has development tools, APIs, and samples.
 * You can use Dart for web apps and command-line apps.
 * Run Dart web apps directly in Dartium.
 * Compile Dart apps to JavaScript for other browsers.
 * All Dart apps have a main() function.
 * Dart supports top-level functions.
@@ skipping 573 matching lines @@
 </ul>
 
 ##What next?
 
 The next tutorial, [Connect Dart & HTML](/docs/tutorials/connect-dart-html/),
 steps you through writing a tiny web app from scratch.
 
 {% endcapture %}
 
 {% include tutorial.html %}