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.
WindowH is not tooltip height, it's height of the hole Dynamo window. It's used to place tooltip at the right place, when it's not possible to locate tooltip near the top of item that called it. So, I think it's not so easy to hard code this value in Configuration.cs, because Dynamo window can every moment change its height.