Simplify Overseer invocation

[asubb]

Assuming outputs

val output1 = stream.out{ }
val output2 = stream.out{ }

Initiate the overseer

val execution =
  // single threaded serial execution
  // for a set of outputs
  listOf(output1, output2).serialExecution()
  // or for singular output
  output1.serialExecution()

  // multithreaded parallel execution
  // for a set of outputs
  listOf(output1, output2).parallelExecution(threads = 2, partitions = 2)
  // or for singular output
  output1.parallelExecution(threads = 2, partitions = 2)

  //distributed execution
  // for a set of outputs
  listOf(output1, output2).distributedExecution(facilitators = ..., partitions = 2)
  // or for singular output
  output1.distributedExecution(facilitators = ..., partitions = 2)

And then execute it

// asynchronously
val future = execution.async()
// or synchronously
execution.sync()