Added support for Native environments

In this release we added support for native environments. This service might be used in the "sync" mode, to trigger "focused" state changes after native engine sets the focus to some elements. In this mode the only way to set the focus is to use stealFocus method. setFocus method is disabled. Also certain "imperative" features like layout measurements, coordinates calculations etc. are disabled because the native engine is the only one who decides what to focus. Please read the documentation for examples of usage in Native mode.