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/peers.c b/src/peers.c
index 633f9ae..933f8ba 100644
--- a/src/peers.c
+++ b/src/peers.c
@@ -30,6 +30,7 @@
 #include <haproxy/net_helper.h>
 #include <haproxy/obj_type-t.h>
 #include <haproxy/peers.h>
+#include <haproxy/proxy.h>
 #include <haproxy/task.h>
 #include <haproxy/session-t.h>
 #include <haproxy/signal.h>
@@ -40,7 +41,6 @@
 #include <haproxy/thread.h>
 
 #include <haproxy/fd.h>
-#include <proto/proxy.h>
 #include <proto/stream.h>
 #include <haproxy/stick_table.h>