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/hlua.c b/src/hlua.c
index bed059c..0d3a3e9 100644
--- a/src/hlua.c
+++ b/src/hlua.c
@@ -21,6 +21,7 @@
 #error "Requires Lua 5.3 or later."
 #endif
 
+#include <haproxy/applet.h>
 #include <haproxy/api.h>
 #include <import/ebpttree.h>
 
@@ -51,7 +52,6 @@
 #include <types/stats.h>
 
 #include <haproxy/arg.h>
-#include <proto/applet.h>
 #include <proto/channel.h>
 #include <proto/cli.h>
 #include <proto/stats.h>