Refactor sampled test queries into a separate abstract class
Distribute splits evenly among nodes
Experimental support for approximate queries

Currently only AVG is supported. The syntax is:
SELECT AVG(a)
FROM my_sampled_table
APPROXIMATE AT 95.0 CONFIDENCE

This is disabled by default, but can be enabled with the config option analyzer.approximate-queries-enabled=true
Ensure all page buffer clients are closed
Update to latest airbase, airlift and discovery
Move TestingPrestoServer from test to main
Make primary JDBC artifact standalone
Fix LocalExecutionPlanner handling of null literal projections

Disable compiler tests involving untyped nulls and mixed numeric types
Move Input from client to presto-main

It's not needed by the client (yet). We may move it back later if we decide to expose
this info to clients in a structural way
Rewrite of hive SerDeUtils.getJSONString() using jackson.
Rename HashJoinOperator => LookupJoinOperator
Add support for index joins