Add ZooKeeper to SBT library dependencies.
Launch ZooKeeper server on play startup.

Also add a sample ZooKeeper configuration file: zoo.cfg.
Launch ZooKeeper server through an Actor.

- Change ZooKeeperLauncher to an Actor.
- Add two commands: Launch and Shutdown.
Move import of play.api.Play.current to where it is used.

Because play.api.Play.current is used as implicit, it is better to minimize the
scope.
Extract parameters to BeyondContextFactory as BeyondContextFactoryConfig.

Encapsulate all configuration parameters into one class.
Add curator-recipes to SBT library dependencies.
Build fix.

[error] /home/travis/build/SollmoStudio/beyond/app/beyond/plugin/GamePlugin.scala:18:
not enough arguments for constructor BeyondContextFactory: (config: beyond.plugin.BeyondContextFactoryConfig)beyond.plugin.BeyondContextFactory.
[error] Unspecified value parameter config.
[error]   private val contextFactory: BeyondContextFactory = new BeyondContextFactory
[error]                                                      ^
Rename ZookeeperLauncherCommand to ZooKeeperLauncherCommand.
Launch MongoDB server.

Add MongoDBLauncher actor which manages the lifecycle of MongoDB server.
Override Actor lifecycle methods to launch and shutdown server.

The lifecycle of the underlying server is always the same as that of its actor.
So there is no need for separate Launch or Shutdown messages.
Use time unit seconds in timeout value.

It is more readable to use time units such as seconds in timeout value.