TAJO-1128: Implement a select box for database at web interface. (Jongyoung Park via hyunsik)

Closes #222
Merge branch 'master' of http://git-wip-us.apache.org/repos/asf/tajo into index_support
Merge branch 'index_support' of http://git-wip-us.apache.org/repos/asf/tajo into TAJO-838_3