Added timestamp to log pane

Added a timestamp to the log pane as per #225. The formatting options on the Java HTMLEditorKit are pretty limited so I couldn't put the timestamp on the right... I've put it on the left in grey instead:

![screen shot 2014-04-06 at 2 58 46 pm](https://cloud.githubusercontent.com/assets/1667484/2624540/f281ca8a-bd48-11e3-9548-a7cbf6b77295.png)