REORG: include: move proxy.h to haproxy/proxy{,-t}.h

This one is particularly difficult to split because it provides all the
functions used to manipulate a proxy state and to retrieve names or IDs
for error reporting, and as such, it was included in 73 files (down to
68 after cleanup). It would deserve a small cleanup though the cut points
are not obvious at the moment given the number of structs involved in
the struct proxy itself.
diff --git a/src/frontend.c b/src/frontend.c
index 8252c81..78dc964 100644
--- a/src/frontend.c
+++ b/src/frontend.c
@@ -28,6 +28,7 @@
 #include <haproxy/frontend.h>
 #include <haproxy/http_ana.h>
 #include <haproxy/log.h>
+#include <haproxy/proxy.h>
 #include <haproxy/sample.h>
 #include <haproxy/stream_interface.h>
 #include <haproxy/task.h>
@@ -39,7 +40,6 @@
 #include <haproxy/arg.h>
 #include <haproxy/fd.h>
 #include <haproxy/proto_tcp.h>
-#include <proto/proxy.h>
 #include <proto/stream.h>
 
 /* Finish a stream accept() for a proxy (TCP or HTTP). It returns a negative