wayland: internal event buffer & wait for xdg configure

[elinorbgr]

This PR does three things:

• fix Wayland panic with renderer #254 by properly waiting for the configure xdg event from the compositor, this is done by introducing an internal buffer to collect events dispatched internally, while Window::new() may be blocking
• automatically insert a WindowEvent::Refresh in this internal buffer whenever a window is created, this guarantees the event loop will have something to dispatch when first started, and should solve for good any issue of deadlock of the event loop as previously saw with wayland (without that, the multiwindow example of glutin still deadlocked)
• update the wayland_window dependency, which provides a better handling of said configure event

[tomaka]

Triage. I guess there's no reason not to merge this.