Make explicit runners only available for emit

After #136 we're using namespace when you specify a particular runner, e.g. `widget.publish("foo:hub_sequence")`, which makes it ambiguous in case you make call like `widget.pubilsh("foo:sequence")` where the runner is not really fit the method behavior.

We shall limit the explicit runner feature to be handled only by the basis method "emit", while enforcing a particular runner high-level methods like "publish" (which shall use the pipeline runner), which basically **use different method names to present runner type**.