CONTRIB: move src/da.c and contrib/deviceatlas to addons/deviceatlas

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, github build matrix, coverity checks
and travis CI's build were updated.
diff --git a/doc/DeviceAtlas-device-detection.txt b/doc/DeviceAtlas-device-detection.txt
index bb4e369..9a1c9b5 100644
--- a/doc/DeviceAtlas-device-detection.txt
+++ b/doc/DeviceAtlas-device-detection.txt
@@ -13,12 +13,12 @@
 
 For HAProxy developers who need to verify that their changes didn't accidentally
 break the DeviceAtlas code, it is possible to build a dummy library provided in
-the contrib/deviceatlas directory and to use it as an alternative for the full
-library. This will not provide the full functionalities, it will just allow
+the addons/deviceatlas/dummy directory and to use it as an alternative for the
+full library. This will not provide the full functionalities, it will just allow
 haproxy to start with a deviceatlas configuration, which generally is enough to
 validate API changes :
 
-    $ make TARGET=<target> USE_PCRE=1 USE_DEVICEATLAS=1 DEVICEATLAS_SRC=$PWD/contrib/deviceatlas
+    $ make TARGET=<target> USE_PCRE=1 USE_DEVICEATLAS=1 DEVICEATLAS_SRC=$PWD/addons/deviceatlas/dummy
 
 These are supported DeviceAtlas directives (see doc/configuration.txt) :
   - deviceatlas-json-file <path to the DeviceAtlas JSON data file>.