First version of new item notification.

    The FeedApplet now has a new_item_notification method. It is passed to
    the FeedReader objects as a callback and is invoked when new items arrive.
    This behaviour is surpressed during startup.
Fixed notifications.
Notifications settings entry
Fixed notification settings.
No notifications on startup
Changed text for new item
Some refinements to notification system:

    * using this.path instead of determining every time a notification is sent

    New notification content:
    * if a feed has only a single unread item, we display the title of the item
    * Otherwise we display the total number of unread items.

    * Removed the startup check, resulting in unread items to be displayed at startup
Removed "test notification" context menu entry
Merge pull request #40 from NiklasMM/master

Unread items notifications