Change API: Reader.getCurrent() should always return IndexedRecord and Writer.write() should accept IndexedRecord

Following API changes should be made (potentially breaking):

1. T Reader.getCurrent() throws NoSuchElementException -> IndexedRecord Reader.getCurrent() throws NoSuchElementException
2. void Writer.write(Object object) throws IOException -> void Writer.write(IndexedRecord record) throws IOException

Before we allowed any object for optimization reason in case of specific job design:
tSomeFamilyInput -> tSomeFamilyOutput (both from the same family)
It was found it wasn't used. Also we still may have such optimization if component extends IndexedRecord and put its native object there. Output component may try to cast incoming IndexedRecord to its specific type and retrieve native object