added monitor capabilities to support configuration update in clustered ...

...environment - currently deployments only

Extension to ConfigurationService to monitor underlying system repository for changes. In case a change is discovered notifies interested parties to perform update. Currently this mechanism is only used by deployments config service to be able to propagate deployments across cluster, once git repository is synchronized monitor will trigger runtime changes so all servers in the cluster will becomes in sync.

Monitor is enabled by default but can be disabled with system property. Interval of how often monitor checks the repository is also configurable - by default 2 secs.

Monitor checks the last modified date of a single file that is updated on every configuration change.