Moved all FileSystem-related classes to io package.

Functionality used from ConfigurationUtils was switched to be called from
FileLocatorUtils. Some methods which now caused compilation errors in
ConfigurationUtils (because FileUtils was moved, too) have been deleted (they
are replaced by corresponding methods in FileLocatorUtils).

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1521603 13f79535-47bb-0310-9956-ffa450edef68