Make PMode class static

[phax]

Thanks Philip. FWIW, I think that it would be best if the PMode class and all of its subclasses were to be concrete. The reason I say this that PModes are something that we want to marshal/demarshal (serialize/deserialze). We want to store them on the file system, in databases, we want to pass them on Kafka streams and MQ queues, etc. Each of the ways that we want to store and/or transport PModes has well known utilities that can directly operate on concrete objects and marshal/demarshal (serialize/deserialze) them. Jackson data-bind, GSON, JAXB, JDBC, Java serialization, etc. If the class and/or its subclasses are not concrete, then it is more complicated and non-standard.

[phax]

Part of 0.12.0