Removes jackson-utils dependency.

In order to remove Google Guava from as dependency, we thought that instead of removing from jackson-utils and then adapt the code of two projects, it could be better to update to Jackson 2.4 which already implements JsonPointer. 

We know that this change is a big change and the leader of the project may decide to reject the PR because of this.

For our case and for our business it fits perfectly to use Jackson 2.4,but we fully understand that this it may not  be perfect for other cases.

Anyway we decided to send a PR because maybe the leader of the project may find it useful and can be accepted or do some code review to make it happens on upstream project.  If not and following the ASL2.0 license we modified the code and made it available on our public github for anyone who wants to use it.

As I said our main intention is to merge this change to upstream repo.
Jackson applies a JSonPointer over a JsonNode and not the inverse as used in jackson-utils.
Moreover Jackson JsonPointer does not implement the parent method. For this reason we have created  a head method which do exactly the same as parent() method but using Jackson JsonPointer.

Side note: we have sent a PR to jackson-core to add support for head() method natively.