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.
Merge commit 'aa5e3b683120a8b1841c523232b7a8a28371e7c9' into TAJO-1128