Format hours in FormattingUtils

Eurgh, I really hate this code. And funnily enough line breaks *before* a minus
sign will just silently break. A line starting with "-" is going to be ignored.
WTF?
Groovy lists have a `groupBy` method like Scala. The following gets you a map of timestamps to list of execution times.

```
Map times = lines.groupBy { it[0] }
```