Load options page bar preview upon DOM ready.

Apparently switching on CSP caused the iframe content to be unable to
access chrome.extension. Loading the iframe after the options page DOM
seems to work around this issue.

src/options.html

@@ -13,7 +13,7 @@
     <h1><img src="/images/shine.svg" alt="logo"/>reddit companion options</h1>
     <div id="contents">
       <section class="bar">
-        <shinebar><iframe src="bar.html#_shine_demo"></iframe></shinebar>
+        <shinebar><iframe></iframe></shinebar>
         <div class="options">
           <ul>
             <li class="showPageActionLine"><input type="checkbox" id="showPageAction"> <label for="showPageAction">display icon in address bar</label></li>

src/options.js

@@ -1,4 +1,6 @@
 $(document).ready(function() {
+  $('shinebar iframe').attr('src', chrome.extension.getURL('bar.html') + '#_shine_demo')
+
   var messages = [
     'greetings, human.',
     'someone is wrong on the internet!',