#ZATS-11:
 * client support piggyback event
 * implement echo event handler
 * add test cases for echo events
Merge branch 'ZATS-11' into dev
Merge remote-tracking branch 'origin/dev' into dev
ZATS-11:
 * separate echo event handler into ZK 5 and 6
 * register version checking support wildcard at sub-version
 * fix duplicate handler register in ZATS-Ext6
 * fix example project pom.xml issue
 * fine-tune test cases