Add watched indicator to photo albums

[Jelmer van der Linde]

Keep track of which photo albums users have already seen and which are new. Similar to the forum topics which are marked when there is a new post.

[Jelmer van der Linde]

Read status tracking and displaying implemented in 839de11106d2b726f02ad15f07502df25fd21b02. However, I'm not yet satisfied with the result: now all the books you haven't opened are marked as "new". (You can easily mark them as read using the button, but that is an action nobody is going to take.)

[Jelmer van der Linde]

In dcd263780603f667b3e428cba35e56b8f84de1b8 I've implemented that the new indicator only appears for books published after the 1st of September of a member's 'beginjaar'.