Unobtrusive updates

This is a followup to #5 and #6, where @borkweb and @zbtirrell shared a lot of ideas and patches.

Currently when a normal user has a liveblog open and there's a new entry, they see a nag with the number of new entries:

![Screen Shot 2012-12-20 at 14 05 18 ](https://f.cloud.github.com/assets/27954/24326/d1a7f9d4-4a9d-11e2-904c-f0cf27ae42d0.png)

Having to click for each update while following a fast-paced event, or when the user left the liveblog open on a secondary display can quickly get annoying.

The original reason the nag was implemented were two:
* If there are a bunch of new entries, the user may get lost and don't know which entries are new and which old.
* Automatically adding new entries messes up with the scroll.

We need to solve this in an unobtrusive way – no action from the user should be required if they haven't scrolled, if they have – going back to the new entries should be easy.

P.S. This is a second attempt, after #62, which was mysteriously merged.