Prevents VUFIND-839 from breaking createHierarchyTrees.php util.

Resolves VUFIND-839.

Resolves VUFIND-838.

Resolves VUFIND-835; thanks to Luke O'Sullivan for the fix.

Resolves VUFIND-107.

Thanks to David Maus for refactoring suggestions.

The Service is setup in VuFind main module, the module does nothing
special except providing the classes and an autoloader configuration.

Thanks to Clemens Kynast and Michael Wiesen for development work.

Thanks to Arek Danszczyk and Christian Dabrowski.