Support async jobs

[swarmshine]

interface DistributedJob{
   void run(context: Context)
}

currently supports sync launching and execution.
Actually there are many cases when jon maintain it's own thread pool and execute work items in async way

void run(context: Context){
    context.workShare.map{ processAsync(it) }.forEach{ it.join()}
}

This leads to wasting resources for extra Threads.
Solution is to support async job invocation

interface DistributedAsyncJob{
   CompletableFuture<Void> run(context: Context)
}
``