REORG: applet: move the applet definitions out of stream_interface

We're tidying the definitions so that appctx lives on its own. A new
set of applet.h files has been added for this purpose.
diff --git a/include/proto/dumpstats.h b/include/proto/dumpstats.h
index 61e39bf..cbbb802 100644
--- a/include/proto/dumpstats.h
+++ b/include/proto/dumpstats.h
@@ -24,6 +24,7 @@
 #define _PROTO_DUMPSTATS_H
 
 #include <common/config.h>
+#include <types/applet.h>
 #include <types/stream_interface.h>
 
 /* Flags for applet.ctx.stats.flags */