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

The type file was slightly tidied. The cli-specific APPCTX_CLI_ST1_* flag
definitions were moved to cli.h. The type file was adjusted to include
buf-t.h and not the huge buf.h. A few call places were fixed because they
did not need this include.
diff --git a/src/peers.c b/src/peers.c
index cba840d..1d60e3f 100644
--- a/src/peers.c
+++ b/src/peers.c
@@ -20,6 +20,7 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 
+#include <haproxy/applet.h>
 #include <haproxy/api.h>
 #include <haproxy/dict.h>
 #include <haproxy/frontend.h>
@@ -35,7 +36,6 @@
 
 #include <types/stats.h>
 
-#include <proto/applet.h>
 #include <proto/channel.h>
 #include <proto/cli.h>
 #include <haproxy/fd.h>