Refactor notification feed: modify the way how feed creates links to each object

[w32blaster]

At this moment each object has the following link in the feed message:

def href = g.createLink(controller: classSimpleName, action: 'show', id: actorObject.ident(), absolute: true)

Sometimes we need to change this behaviour. Especially for comments.

Todo

• add new method to INotifiable interface, let's say getLink
• implement for each implementation this method. Pay attention to the comments and repository
• when open comments, we need to distinguish Comments and Replies
• add permalinks for comments