Initial commit, a working component for Sling announcing its config and endpoints to ZooKeeper.

Config is for now passed via "sling.config" system property, ZooKeeper connection string via "zookeeper.connString" property (localhost:2181 is used if null).
Moved ZK functionality to a separate ZooKeeperConnector class.
Fixed check for node creation, added the originally intended watch on it.
Moved ConfigAnnouncer to org.apache.sling.devops.api.instance package, and ZooKeeperConfigAnnouncer to org.apache.sling.devops.zookeeper.instance package.
Moved sling-config-announcer project contents to root, renamed it to org.apache.sling.devops (potentially to be split into several projects in the future).
Removed "api" path from package name.
Updated project name in pom.