Support create/ensure for channels and actors

NOTE: This breaks the old wes_channel API

* Adds a new public API to the wes module
* Support both create and ensure for channels and actors
  (create produces an error when a channel/actor already exists, ensure
   just makes sure it exists).
* Channels and actors are now two-tuples
* Actor specifications now must have a start type (create or load)
* Added types and dialyzer fixes