Disgusting implementation of a performance-friendly feed renderer.

This one does not pull every single message of each and every followee into a set before rendering the first 20. Instead, it pulls only the next available message from each followee, picks the first one by timestamp, adds it to a list, tosses it and repeats.
Made the code Java 7-compatible.

Still uses JSR 310, but otherwise, it compiles against JDK 7.