[client] x11: Add inline icon

Many X11 window managers will present an application on their
taskbar as a combination of the application name and an icon
imagery pulled from the X-Property _NET_WM_ICON. Applications
built under frameworks such as Qt or GTK have this property
populated by the framework. This commit adds the Atom _NET_WM_ICON
and populates it with a 64x64 icon of Looking Glass.

client/CMakeLists.txt

@@ -107,6 +107,7 @@ add_custom_command(
 )
 
 include_directories(
+	${PROJECT_TOP}
 	${PROJECT_SOURCE_DIR}/include
 	${CMAKE_BINARY_DIR}/include
 )