Layers initial prototype.

Includes  an auto generated layer (GenericLayer) that wraps  all api calls.
Includes a basic handwritten layer (basicLayer)  that wraps a few apis.
Adds xglGetProcAddr as a new api, which is used to chain layers together.
All layers and loader implement  a dispatch table.
diff --git a/icd/common/icd.h b/icd/common/icd.h
index ee68bf1..badef5f 100644
--- a/icd/common/icd.h
+++ b/icd/common/icd.h
@@ -32,6 +32,7 @@
 
 #include <xgl.h>
 #include <xglDbg.h>
+#include <xglLayer.h>
 
 #include "icd-dispatch-table.h"