TAJO-1261: Separate query and ddl execution codes from GlobalEngine.

Closes #312
TAJO-1250: RawFileAppender occasionally causes BufferOverflowException. (jinho)

Closes #303
TAJO-1262: Rename the prefix 'SubQuery' to 'Stage'.

Closes #314
Merge branch 'master' into TAJO-1257
TAJO-1259: Change tsql history behavior. (Jaewoong Jung via hyunsik)

Closes #316
TAJO-1249: Tajo should check if a file format given in DDL is supported. (DaeMyung Kang via hyunsik)

Closes #313
TAJO-1268: tajo-client module should not use UserGroupInformation.

Closes #318
TAJO-1267: Remove LazyTaskScheduler. (DaeMyung Kang via jihoon)
TAJO-1266: Too many logs when writing a parquet relation. (DaeMyung Kang via jihoon)

Closes #320
TAJO-920: Add FIRST_VALUE and LAST_VALUE window functions. (Keuntae Park via hyunsik)

Closes #308
Merge branch 'master' into TAJO-1257