Add a Blog List tab that shows all subscribed blogs
This ticket depends on #409 (closed) and #413 (closed).
When a blog from Available Blogs (#413 (closed)) has been clicked, it will be added to the "Blog List" tab. Here all subscribed blogs should be shown.
Phase 1
Order:
(1) unread messages with latest posts first (2) date of last post
Phase2
Implement possibility to pin an element to the top
Order:
(1) pinned blogs (2) unread messages with latest posts first (3) date of last post