Added very basic client error handler. And basic test.

On a routing error, the router will trigger "action:error", similar to "action:start" and "action:end".

Example usage:

// Rendr controller:
function(params, callback){
  if (!params.specialValue)
    return callback(status: 404);
  callback(null, params.specialValue);
}

// client code to handle exception
App.router.on("action:error", function(err, route) {
    // console.error("Routing error", err, route)
  }
});
Merge pull request #122 from juvo-tv/handle_client_routing_errors

Added very basic client error handler. And basic test.