Add ToChildStart typeclass. #DPP-81

* Replaced closureToChildStart and processToChildStart functions with ToChildStart

  Now in order to create a ChildStart from a (Process ()) we don't need the supervisor pid,
  we link the restarter and the supervisor process once we get a message from the supervisor with
  the triple (ProcessId, ChildKey, SendChan)

* Renamed function wrapChanProcess to wrapRestarterProcess