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/session.c b/src/session.c
index 4169870..7066a8f 100644
--- a/src/session.c
+++ b/src/session.c
@@ -17,11 +17,11 @@
 #include <haproxy/listener.h>
 #include <haproxy/log.h>
 #include <haproxy/pool.h>
+#include <haproxy/proxy.h>
 #include <haproxy/session.h>
 #include <haproxy/tcp_rules.h>
 #include <haproxy/vars.h>
 
-#include <proto/proxy.h>
 #include <proto/stream.h>
 
 DECLARE_POOL(pool_head_session, "session", sizeof(struct session));