Renamed *Handler classes to *Utilities classes and moved them into their
own util package
Methods that throw checked exceptions now correctly declare so;
update javadoc for methods that read and write from/to files, now state
that they throw IllegalArgumentExceptions if the given file does not
exist
removed mistake in JDoc comment for writeFile() -- if the file does not
exist it makes and writes to it rather than throw an exception
Created test class for DataUtilitiesXmlImpl, plus the appropriate mock
methods in DataUtilitiesXmlImpl for unimplemented methods