TAJO-1177: Reduce the use of Sun proprietary API. (Jihun Kang via hyunsik)

Closes #243
TAJO-1172: Remove Trevni storage type and its related classes (DaeMyung Kang via hyunsik)

Closes #244
TAJO-1184: Upgrade netty-buffer to 4.0.24.Final. (jinho)

Closes #248
TAJO-1178: Some error messages for wrong JSON queries are not so much helpful. (Jaewoong Jung via jihoon)