Option to import bookmark folders as tags

There is no standard way of export tags in Netscape's bookmarks file format. When exporting from Google Bookmarks, folders are used as tags. The following example shows a bookmark that was tagged with **Programming** and **History**:

```html
<!DOCTYPE NETSCAPE-Bookmark-file-1>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=UTF-8">
<TITLE>Bookmarks</TITLE>
<H1>Bookmarks</H1>
<DL><p>
  <DT><H3 ADD_DATE="1258826211990949">Programming</H3>
  <DL><p>
    <DT><A HREF="http://dotnetmasters.com/historyofcfamily.htm" ADD_DATE="1260914469588170">History of the C family of languages</A>
  </DL><p>
  <DT><H3 ADD_DATE="1238826211990949">History</H3>
  <DL><p>
    <DT><A HREF="http://dotnetmasters.com/historyofcfamily.htm" ADD_DATE="1260914469588170">History of the C family of languages</A>
  </DL><p>
</DL><p>
```

In order to support imports from Google Bookmarks (and other services which use folders during the export), I added an option to the import form which does the trick.