The DateUtil class provides some of the same functionality that is already available in Joda Time, which is being used by 'dna-graph'. Since this class is used very little (really, just by the tests and by StringUtil.readableString methods), we should just remove the DateUtil class.

Also, by ensuring that Property.toString() returns a readable string, and that the Value classes all have readable toString() methods, then we can use List.toString(), Set.toString(), Property.toString(), and Map.toString(). The toString() method on arrays is crappy, but this can easily be fixed by using "Arrays.asList(array).toString()". This means that we can then delete the StringUtil.readableString(...) methods.