Adding condition to unmount only components that already not in the Document object.

[vitalii-onopriienko]

Adding condition to unmount only components that already not in the Document object.

This will resolve issue when after execution  app.unmount() on page all components that have return functions are unmounted (deleted from app cache and all events and event listeners for them are removed) but after app.mount() nothing happening (all stayed exactly alike after unmount).

With new changes after app.unmunt() we are unmounting only components that already not in Document object. So in case when after we changed our document by removing some of components and adding new ones by js we safely able to run app.unmount() and app.mount(). In this case, only already removed components will be unmounted and new one will be mounted.

[carolirod]

Please merge! 😃