Disable POJO types

@StephanEwen, @aljoscha: Can someone please confirm that this is the place to disable the POJO types?

There are various issues when working with POJOs in the Java API, for example [1].

[1] https://mail-archives.apache.org/mod_mbox/incubator-flink-dev/201407.mbox/%3C53D96049.1060509%40cse.uta.edu%3E