REORG: include: move common/fcgi.h to haproxy/

The file was moved almost verbatim (only stdio.h was dropped as useless).
It was not split between types and functions because it's only included
from direct C code (fcgi.c and mux_fcgi.c) as well as fcgi_app.h, included
from the same ones, which should also be remerged as a single one.
diff --git a/include/types/fcgi-app.h b/include/types/fcgi-app.h
index 72219e9..c82f39a 100644
--- a/include/types/fcgi-app.h
+++ b/include/types/fcgi-app.h
@@ -24,7 +24,7 @@
 
 #include <haproxy/api-t.h>
 #include <import/ist.h>
-#include <common/fcgi.h>
+#include <haproxy/fcgi.h>
 #include <haproxy/list-t.h>
 #include <haproxy/regex-t.h>