New feed_file features: Custom title, comments and edit from context menu

Hey, I've got some new features for the feed file, to make it more convenient to use.
(I have a feed with a ridiculously long title, which gave me the idea to the custom titles :-) )

    * Added "edit feed file" context menu entry which launces gedit with the feed file
    * Added comment support for feed file: lines starting with '#' will be ignored
    * Added custom title support: The user can specify a custom title for each feed to be displayed instead of the RSS title:
        <feed_url> <custom_title>