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/include/proto/backend.h b/include/proto/backend.h
index f702be9..57d606e 100644
--- a/include/proto/backend.h
+++ b/include/proto/backend.h
@@ -23,10 +23,10 @@
 #define _PROTO_BACKEND_H
 
 #include <haproxy/api.h>
+#include <haproxy/proxy-t.h>
 #include <haproxy/time.h>
 
 #include <types/backend.h>
-#include <types/proxy.h>
 #include <types/server.h>
 #include <types/stream.h>