Fix issue with drag n drop over lazy loaded nodes

[megaboich]

PR to fix issue #211
Also added example of loading nodes dynamically during expand.

Issue is very well easy to reproduce when you try to drag some node over those which is not loaded yet. Unhandled exception is thrown and application turns into white page.

Personally I don't really like the solution, it seems that there should be better way to fix it, but now it is stable and working.

[wuweiweiwu]

@megaboich react 16 has the lifecycle function componentDidCatch you can possibly do the error handling there.

If you can fix the conflicts that'll be awesome :)

Also i will be experimenting with the new react 16-3 alpha to see if we can use Suspense

[megaboich]

@wuweiweiwu
I think it would better to create new PR just for example of lazy-loading data and also provide some better documentation about this whole functionality.

Next step would be to fix actual issue with drag and drop.

What do you think?

[wuweiweiwu]

@megaboich I apologize for the late response. I think that would be a great idea!

A PR would be much appreciated.

#278 seems to be related to the drag and drop issue

[megaboich]

Well, it seems we have quite slow progress here, but anyway I am going to close this PR and create new one with just an example of lazy loading during expand.