Dump reworked AC support for rpi

Add two patches for rpi-userland and webkitgtk that contain the current work-in-progress for advancing the accelerated compositing for WebKitGTK+ under Wayland, on Raspberry Pi.

The webkitgtk-shell package is also added, providing the /usr/bin/webkitgtk-shell program which simply creates a WebKitGTK+ widget and displays it in fullscreen.