Fix some typos, broken links and other issues in extension docs

chrome/common/extensions/docs/templates/articles/app_architecture.html

 <meta name="doc-family" content="apps">
 <h1>Understand the Architecture</h1>
 
 
 <p>
 Packaged apps integrate closely with a user’s operating system.
 They are designed to be run outside of a browser tab,
 to run robustly in offline and poor connectivity scenarios and
 to have far more powerful capabilities than are available
 in a typical web browsing environment.
@@ skipping 71 matching lines @@
 <br>
 
 <table class="simple">
   <tr>
     <th scope="col"> Stage </th>
     <th scope="col"> Summary </th>
   </tr>
   <tr>
     <td>Installation</td>
     <td>User chooses to install the app and explicitly accepts the
-        <a href="manifest.html#permissions">permissions</a>.
+        <a href="declare_permissions.html">permissions</a>.
     </td>
   </tr>
   <tr>
     <td>Startup</td>
     <td>The event page is loaded,
       the 'launch' event fires,
       and app pages open in windows.
       You 
       <a href="app_lifecycle.html#eventpage">create the windows</a>
       that your app requires,
@@ skipping 61 matching lines @@
 You can use the <code>object</code> tag to
 <a href="app_external.html">embed external content</a>;
 this content runs in a separate process from the app.
 </p>
 
 <p>
 <iframe title="YouTube video player" width="610" height="380" src="http://www.youtube.com/embed/EDtiWN42lHs" frameborder="0" allowfullscreen></iframe>
 </p>
 
 <p class="backtotop"><a href="#top">Back to top</a></p>