Fixes #196

Return InvalidAppMaster if Class.forName fails. This message will be stored in the AppManager.appMasterRegistry and returned to the client when the client issues a ShutdownApplication(appId) so the client knows why the appmaster failed. Note we need to account for some sort of history server so an audit log exists similar to YARN's history manager and tracks all appmasters execution. This will be addressed is a subsequent issue opened.
Also upgraded akka to 2.3.8 which removes some bogus disassociated messages.

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```the normal pattern of always going through the master -> appmanager```

It is only true for external service, like worker, client, and appmaster, as Master is the sole interface for those services.

For internal actor of AppManager, we prefer to talk to appmanager directly.