carry over container property to popup

Bootstrap popups have issues with tables, which means that bootstro has issues with highlighting a particular column header (for example).  They added the 'container' property to fix this -- this fix just carries over the container property so it can be used in bootstro as well.

Test file I used is below.  Try it without this commit, and you'll see that the second column of the table is pushed to the right when the popup shows up.   With commit, works fine.

```
<html>
  <head>
    <!-- Latest compiled and minified CSS -->
    <link rel="stylesheet" href="http://maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css">

    <!-- Optional theme -->
    <link rel="stylesheet" href="http://maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap-theme.min.css">

    <!-- Latest compiled and minified JavaScript -->
    <script src="http://code.jquery.com/jquery-2.1.1.min.js"></script>
    <script src="http://maxcdn.bootstrapcdn.com/bootstrap/3.2.0/js/bootstrap.min.js"></script>

    <!-- Bootstro -->
    <link href="bootstro.css" rel="stylesheet" type="text/css" />
    <script src="bootstro.js"></script>

  </head>
  <body>
    <div class="container">
      <table class="table">
        <thead>
          <tr>
            <th class="bootstro" data-bootstro-container="body" data-bootstro-content="Test">First</th>
            <th>Second</th>
          </tr>
        </thead>
        <tbody>
          <tr>
            <td>Data 1</td>
            <td>Data 2</td>
          </tr>
        </tbody>
      </table>
    </div>

    <script>
     $(document).ready(function () {
       bootstro.start('.bootstro');
     });
    </script>
  </body>
</html>
```