TAJO-1140: Separate TajoClient into fine grained parts.

Closes #213
TAJO-1114: Improve ConfVars (SessionVar) to take a validator interface to check its input. (Jihun Kang via hyunsik)

Closes #218
TAJO-1145: Add 'bin/tajo --help' command. (Jihun Kang via hyunsik)

Closes #220
TAJO-1133: Add 'bin/tajo version' command. (Jihun Kang via hyunsik)

Closes #219
TAJO-1139: ExternalSortExec should delete the intermediate files. (jinho via hyunsik)

Closes #212
TAJO-1141: Refactor the packages hierarchy of tajo-client.

Closes #217
Fixed missed classpath change of TAJO-1141.
TAJO-1150: Some weird methods in QueryClientImpl should be fixed. (Jongyoung Park via hyunsik)

Closes #223
TAJO-1032: Improve TravisCI scripts to adjust log4j log level. (jinho)

Closes #226
TAJO-1153: Merge off-heap package in block_iteration branch to master branch.

Closes #225
TAJO-1129: Remove hadoop 2.2.0 support. (jinho via hyunsik)

Closes #215
TAJO-1154: TajoCli doesn't pause while running the non-forwarded query. (Hyoungjun Kim via hyunsik)

Closes #227