Added support for PERCENTILES in JDBC driver

[galkk]

Adds PERCENTILE output to JDBC

GET /_opendistro/_sql?format=jdbc
{
  "query": "SELECT percentiles(age, 25.0, 50.0, 75.0, 99.9) age_percentiles FROM peoples"
}

{
  "schema": [{
    "name": "age_percentiles",
    "type": "double"
  }],
  "total": 1,
  "datarows": [[{
    "75.0": 36.5,
    "99.9": 39,
    "25.0": 31.5,
    "50.0": 33.5
  }]],
  "size": 1,
  "status": 200
}

Added new unchecked exception that enables us to say that we clearly know that feature is not implemented (differentiating it from not supported)

Fixes #26

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[arsen-es]

Thanks!