[ion] Ion type annotations not written for scalar and list types on serialization

Creating an issue based on the [Google Groups discussion](https://groups.google.com/forum/#!topic/jackson-user/MO_w7n1oyFs).

Issue: Ion type annotations are not written when using [IonAnnotationTypeSerializer](https://github.com/FasterXML/jackson-dataformats-binary/blob/master/ion/src/main/java/com/fasterxml/jackson/dataformat/ion/polymorphism/IonAnnotationTypeSerializer.java). This is due to un-implemented `writeTypePrefixForScalar` and `writeTypePrefixForArray` methods in the class.

Will see if I can work on a PR, with tests, for the fix.