docs(quickstart): wrap plunker prose in Jade block (#3014)

Author: chalin

public/docs/ts/latest/quickstart.jade

@@ -1,19 +1,18 @@
 block includes
   include _util-fns
-  - var _on_Plunkr = 'on Plunker';
 
 :marked
   Angular applications are made up of _components_.
     A _component_ is the combination of an HTML template and a component class that controls a portion of the screen. Here is an example of a component that displays a simple string:
 
 +makeExample('app/app.component.ts')(format='.')
 
-
-.l-sub-section
-  :marked
-    Try this **<live-example>QuickStart example !{_on_Plunkr}</live-example>** without installing anything.
-    Try it locally with the [***QuickStart seed***](guide/setup.html "Setup for local development with the QuickStart seed")
-    and prepare for development of a real Angular application.
+block qs-src-online-and-local
+  .l-sub-section
+    :marked
+      Try this **<live-example>QuickStart example on Plunker</live-example>** without installing anything.
+      Try it locally with the [***QuickStart seed***](guide/setup.html "Setup for local development with the QuickStart seed")
+      and prepare for development of a real Angular application.
 
 :marked
   Every component begins with an `@Component` [!{_decorator}](glossary.html#!{_decorator} '"!{_decorator}" explained')