make terminate_all more resistant to travis
add Dispatcher actor

The dispatcher is responsible for finding local actors and calling their
methods.

Separating this from the router is more flexible for things like
explicit actor publishing and capabilities.
use a reply id header for replies

Using the call id as the message id of the reply could cause problems.
Better to give each message a unique id, and add a reply id header to
replies.
update example scripts and add a call example