Improve type handling for jdbc sink

The jdbc sink is currently limited to handling the entire payload as a string and converting a single json object to row data. We should improve that and support the following input types:

• LinkedCaseInsensitiveMap (single row)
• List<LinkedCaseInsensitiveMap> (multiple rows as a batch insert)
• JSON string {"ID":74488,"NAME":"Foo","YEAR":"2014"}

  (single row)

• JSON array [ {"ID":74488,"NAME":"Foo","YEAR":"2014"}

  ,

  {"ID":74489,"NAME":"Bar","YEAR":"2014"}

  ] (multiple rows as a batch insert)

• none of the above use payload.toString()

The above matches what the new jdbc source puts out (depending on outputType used)