Changes to the JSON format for a chatlog item.

No more type of "blogpost". Basically everything was a blogpost. So if the type element isn't in the payload, it should behave as what we used to call a blogpost. We still check against the type being blogpost because there are data files out there that have this value in it, at least for now.

When an item is updated it gets two new elements: whenLastUpdate and ctUpdates. If an item doesn't have these, you can assume it hasn't been updated after it was posted. (Trying to keep the size of the item small.)

A change I will make tomorrow when it's clear these changes didn't cause breakage: Add an element to the payload that indicates which editor created the item, wizzy or markdown. 

Here's an example of a JSON version of a chat item (this one).