Add avro support for spark hbase connector

Avro is a popular format for hbase storage. User may want the support natively in the connector.

With the support, user can save serialized avro into hbase table, and then query on top of it using spark sql. The conversion between avro and catalyst datatype will be handled automatically. This is one way of support complex data types. Otherwise, user has to define their own customized Serdes to support complex data types.