Generalize/unify state meta info

Flink currently has a couple of classes that describe the meta data of state (e.g. for keyed state, operator state, broadcast state, ...) and they typically come with their own serialization proxy and backwards compatibility story. However, the differences between those meta data classes are very small, like different option flags and a different set of serializers. Before introducing yet another meta data for timers, we should unify them in a general state meta data class.