Add libwpe a general-purpose library for WPE WebKit

A WebKit port optimized for embedded devices

WPE WebKit allows embedders to create simple and performant systems based
on Web platform technologies. It is designed with hardware acceleration in
mind, leveraging common 3D graphics APIs for best performance.

It is required by webkitgtk 2.6 which is currently being tested.

Obtained from: gnome development repo