Win32: move paste code to g_Windowing
Win32: change GUIDialogKeyboardGeneric to use g_Windowing.GetClipboard
OSX: change GUIDialogKeyboardGeneric to use g_Windowing.GetClipboard
Add GetClipboard method to CWinSystemBase
Modify GUIEditControl to use the new paste code
Merge pull request #3034 from jhsrennie/win_paste

Move paste code to g_Windowing