Add distibuted action

- New module spring-statemachine-cluster which is
  based on spring-cloud-cluster to provide leader
  election.
- Ensemble now has a concept of a leader if implementation
  supports it.
- New DistributedLeaderAction can use leader info to execute
  action only on a leader.
- Tweak web sample with these new concepts.
- Fixes #176

gradle.properties

@@ -1,6 +1,7 @@
 springShellVersion=1.1.0.RELEASE
 springSecurityVersion=4.0.3.RELEASE
 springDataRedisVersion=1.6.2.RELEASE
+springCloudClusterVersion=1.0.0.RC1
 jedisVersion=2.7.3
 junitVersion=4.12
 springVersion=4.2.4.RELEASE