Merge branch 'release/v1.5' into develop
rename handler to watcher.
update log4j.xml.

rename appender
set logger's log level to trace
add test case.
rename spring configuration file.
refactor.

rename zkleaderwatcher to zkelectionlistener
zkleader supports methods now
add method to shutdown all leader selector.
add method to start all leader selector.
add leader election support.

remove shutdown and start method in ZkContext
finish leader election test case
Merge branch 'feature/leader_election' into develop
bump version.
log with debug level.
refactor.
Merge branch 'release/v1.6'