Broke the project down into three modules:
* common (shares common functionality of instance and orchestrator)
* minion (instance functionality)
* orchestrator (orchestrator functionality)
Added hashCode() and equals() to Instance
InstanceListeners need to implement AutoCloseable to close resources in close().
Added initial implementation of Orchestrator elements:
* Orchestrator is the main orchestrating component which interconnects an InstanceListener, an InstanceManager, and a ConfigTransitioner.
* ZooKeeperInstanceListener is an implementation of InstanceListener that listens to instance announcements on ZooKeeper.
* ModProxyConfigTransitioner is an implementation of ConfigTransitioner which reconfigures the httpd mod_proxy module to point to new instances.

Notes:
* httpd, mod_proxy, and mod_proxy_balancer must be installed (maybe some other modules as well)
* httpd.conf must "Include" a separate config file inside its <Proxy> directive. This separate config file will contain the BalancerMember list.
* To restart httpd usually a sudo password is required. It can be provided as a parameter (below), or instead the sudoers file can be edited to include the following line:
	myuser	ALL=(ALL) NOPASSWD: /usr/sbin/apachectl

System parameters:
* sling.devops.zookeeper.connString (ZK connection string; default: "localhost:2181")
* sling.devops.proxy.executable (path to httpd executable; default: "apachectl")
* sling.devops.proxy.configPath (path to the separate proxy config file mentioned above; default: "/private/etc/apache2/mod_proxy_balancer.conf")
* sling.devops.manager.n (N parameter for SimpleInstanceManager, number of instances required for a config before it can be transitioned to; default: 2)
* sudo.password (default: none)
Updated system property strings to the ones mentioned in previous commit.
InstanceManager shouldn't decide whether a config is satisfied or not, that's the Orchestrator's job.
Renamed "instance" package to "minion", moved ZooKeeperConfigAnnouncer to it too.
Renamed ConfigAnnouncer to InstanceAnnouncer.
Added a Minion component, converted InstanceAnnouncer classes to regular classes, which the Minion manipulates.