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.
I'm thinking of merging ```DynamoPopup``` and ```TooltipWindow``` into one class. That means refactor ```TooltipWindow``` and derive it from ```Popup``` instead of ```UserControl```, and name it ```LibraryToolTip```. We really do not need two different classes and I don't see how we can reuse ```DynamoPopup``` for another purposes (even if we do need to reuse, a similar one can be written as it is a very thin class).