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/include/proto/stream_interface.h b/include/proto/stream_interface.h
index e381d84..f17e6ae 100644
--- a/include/proto/stream_interface.h
+++ b/include/proto/stream_interface.h
@@ -24,11 +24,11 @@
 
 #include <stdlib.h>
 
+#include <haproxy/applet.h>
 #include <haproxy/api.h>
 #include <haproxy/connection.h>
 #include <types/stream.h>
 #include <types/stream_interface.h>
-#include <proto/applet.h>
 #include <proto/channel.h>