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/applet.c b/src/applet.c
index 510faad..760ddc3 100644
--- a/src/applet.c
+++ b/src/applet.c
@@ -13,10 +13,10 @@
 #include <stdio.h>
 #include <stdlib.h>
 
+#include <haproxy/applet.h>
 #include <haproxy/api.h>
 #include <haproxy/list.h>
 #include <haproxy/task.h>
-#include <proto/applet.h>
 #include <proto/channel.h>
 #include <proto/stream.h>
 #include <proto/stream_interface.h>