Cleaned up (minor refactoring, removed unused imports) AvroType subclasses
- Implemented a new AvroJArray AvroType subclass for bare arrays
- Implemented a new AvroJArrayIO AvroTypeIO subclass for (de)serialization of bare arrays
- Added a test case to AvroTypeSpec for AvroJArray
- Implemented I/O tests in a new AvroJArrayIOSpec class
-  Added new method ReflectionHelpers.classTagForType for reflective array creation