Implement automatic thread creation for announcements

[itismadness]

For blog posts, there is a box to put in a thread ID (or set to 0 to not use a thread) where if left blank, the site will automatically create a thread for the new blog post. This would be useful to have for announcements as well.

This would insert an automatic link at the bottom of the announcement on the front page that stated "Discuss this announcement here" that then links to that thread ID. It should also have a "[Remove Link]" similar to the blog next to that (and should have a confirmation a la issue #98).

The forum ID to use for these should be added to the config.php / config.template.