CONTRIB: move src/wurfl.c and contrib/wurfl to addons/wurfl

Both the source file and the dummy library are now at the same place.
Maybe the build howto could be moved there as well to make things even
cleaner.

The Makefile, MAINTAINERS, doc, and vtest matrix were updated.
diff --git a/MAINTAINERS b/MAINTAINERS
index ff09b08..878d7e3 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -127,7 +127,7 @@
 
 ScientiaMobile WURFL Device Detection
 Maintainer: Paul Borile, Massimiliano Bellomi <wurfl-haproxy-support@scientiamobile.com>
-Files: src/wurfl.c, contrib/wurfl, doc/WURFL-device-detection.txt
+Files: addons/wurfl, doc/WURFL-device-detection.txt
 
 SPOE
 Maintainer: Christopher Faulet <cfaulet@haproxy.com>