Add isEmpty method to ObjectUtils

In Spring's org.springframework.util.ObjectUtils there's a null-safe isEmpty method that checks whether an object is empty based on its type. If the object is a string it calls String.isEmpty, if it's a collection it calls Collection.isEmpty, etc. I think a similar method would be a really nice addition to org.apache.commons.lang3.ObjectUtils, as it would allow people like me to use it without adding a dependency to Spring or re-implementing the method in our code.