Initial commit for tooltip

Tooltip was made as it assumed to be. As it was expected, tooltip covers Scrollbar and user can not use the scroll with mouse until tooltip is opened. Please review code and close that pull request  https://github.com/DynamoDS/Dynamo/pull/2026 because it was made in the wrong brach. I apologize about that wrong pull request, that will not happen again.
Yes @aosyatnik, and unfortunately the changes you made to ```src\Engine``` will have to be removed completely. UI changes should never go in the ```Engine```. If you can, have a look at ```LibraryCustomization``` class and ```DSCoreNodes_DynamoCustomization.xml``` file, those are outside of both the ```DSCoreNodes.dll``` and ```Engine```, still it is able to change the category name for functions in ```DSCoreNodes.dll```.

Please drop me an email if you have got a minute, we can chat about the solution.