Add showSplash and serverSideDecoration properties

This adds:

showSplash: This is a property to set if and application starts without displaying anything but still connects to the wayland socket or if its defined in the desktop file.

serverSideDecoration: This will be set by xdg-decoration and kde-server-decoration wayland extensions, we will request ssd by default.

The changes to both lomiri and qtmir is on its way