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/dns.c b/src/dns.c
index bcbc435..dd29d27 100644
--- a/src/dns.c
+++ b/src/dns.c
@@ -29,6 +29,7 @@
 #include <haproxy/errors.h>
 #include <haproxy/http_rules.h>
 #include <haproxy/log.h>
+#include <haproxy/proxy.h>
 #include <haproxy/sample.h>
 #include <haproxy/stats-t.h>
 #include <haproxy/stream_interface.h>
@@ -44,7 +45,6 @@
 #include <haproxy/fd.h>
 #include <proto/server.h>
 #include <haproxy/proto_udp.h>
-#include <proto/proxy.h>
 
 struct list dns_resolvers  = LIST_HEAD_INIT(dns_resolvers);
 struct list dns_srvrq_list = LIST_HEAD_INIT(dns_srvrq_list);