Fixing popup focus behavior and DPI transform bug.

Fixing the popup behavior and dpi bug

Popups did not behave the same as chrome popup because of how the mouse was captured. I needed to add custom events to mousein and mouseout on the popup to set focus and capture mouse on the popup hwnd instead of the parent.

#213 - Simply refactoring a little and adding the transform to the popup on creation fixed the scaling issues when the window DPI was changed. 

(PS. separating pull request in #313)