Fix some issues after adding sticky headers

[bwindels]

• remove debug logging saying formatRelativeDate
• GapTile.notifyVisible doesn't seem to be called anymore when the viewport isn't filled after opening the timeline. The symptom of this is that at the top of the timeline it says "Not loading" and indeed scrolling doesn't trigger the timeline to be loaded any further. I've checked that programmatically calling notifyVisible on the GapTile from the console loads the timeline again. This is a critical issue, as there is no workaround to access earlier history.
• need to update relative dates after midnight otherwise today is labeled as tomorrow if you leave your client open until the next day