Handle INT96 more gracefully in parquet-avro

The parquet-avro library does not support INT96 columns (PARQUET-323), and any attempt to process a file containing such a column results in:

throw new IllegalArgumentException("INT96 not implemented and is deprecated");

INT96 is still used in many legacy datasets, and so it would be useful to be able to process Parquet files containing these records, even if the INT96 values themselves aren't rendered.

The same functionality has already been re-added into parquet-pig (PARQUET-1133).