Added ConfigLoader for custom configurations in RemoteExecutor 

Ok, 
this is a simple problem. Each implementation of RemoteExecutor may require different settings.
AkkaImpl may need some settings, hazelcast, custom etc.

In order to keep things clearly separated, I suggest the follwing 

abstract class AbstractConfig
trait AkkaConfig extends AbstractConfig
trait DummyConfig extends AbstractConfig

combined with a covariant ConfigLoader trait with an abstract loader  

  def fromConfig(config: C)

which can be mixed in those implementations that require configuration loading 

Comments are in files 
* RemoteExecutor
* Config