DRILL-491: Project pushdown to scan operator.

ProjPushDown: work in progress.  Change to storageplugin and formatplugin

ProjPushDown : Push column name list into scan operator. Got a clean build.

Project pushdown: change from FieldReference to SchemaPath for Hive Scan.

Project Pushdown : handle star column. Add Unit test cases.

Project PushDown : code clean up.