Add support for transient to ShellSurface(Interface)
Review Request #125223 - Created Sept. 14, 2015 and submitted
On client side a setTransient method is added which wraps the semantic of wl_shell_surface_set_transient. On server side both set_transient and set_popup are implemented, though for popup only the transient part is implemented. In particular the grab is not yet handled and also no popup done is provided. For the transient on server side the flags are ignored. Main reason is that Qt does not use the flag, so testing whether it works is tricky (needs a test application).
See extended autotest. Also KWin extended to make use of it: All kind of menus (QMenu, context menu, dropdown) are positioned correctly now.