Issue #431 - Prevent comment link expiry - Added functionality for comment linking

Issue #431 - Prevent comment link expiry - Added functionality for comment linking

*   `media.html`
    *   Changed comment textarea handle from `comment` => `field_comment`
    *   Active comment is hilighted with the CSS class name `comment_active`
    	and also with the hyperlink anchor #comment
    *   Changed media.html so that pagination always uses
    	Route('mediagoblin.user_pages.media_home') as base_url
*   `user_pages/forms.py`
    *   Renamed MediaComment form field `comment` => `field_comment`
*   `user_pages/routing.py`
    *   Added route for `/u/joar/m/123..456/c/234..567/`, points to `media_home`
*   `user_pages/views.py`
    *   `media_home` now checks if the request contains a comment id parameter
        then acts accordingly with pagination whether to call it with a
        `jump_to_id` or not.
    *	`media_post_comment` - Updated MediaCommentForm field name
        `comment` => `field_comment`
*   `util.py`
    *   `redirect` now supports querystring arguments. - NOT USED (should we
        keep it? I think so, it might be useful, sometime [don't call me a
        code hoarder]).
    *   `Pagination.__init__` now accepts one further argument, the `jump_to_id`.
        It assist the comment linking functionality in finding and returning the
        proper page for a comment.
        This feature will work for all kinds of objects. It might not be
        optimal, but it is well functional :)