Add artifact query order by arbitrary resource description property.
The artifact query facility () needs a way to order by arbitrary resource property. The method would likely be called orderByProperty(String propertyHandle) and would use the properties from artifact.getResourceDescription(). Perhaps a separate method orderByProperty(String propertyHandle, boolean missingFirst) would allow artifacts with missing properties to be sorted first, but the default should probably be false; since a property is being specified, it might indicate artifacts with that property are more important than those without.
The following would return images in a "gallery" path relative to the current artifact.