Add ability to short-circuit a method call

[apendua]

E.g.

1. When a method parameters validator returns an error, we can throw immediately instead of sending a message to the server. This is already doable manually, but it would be nice to have a native support for such behavior.
2. Sometimes we may want to simulate a successful method call, e.g. when we want to debounce the final server call, but still have all intermediate state updated in redux store. This is especially useful in all types of editors.