Move part of screenshooter.c to weston-screenshooter.c

This patch splits screensooter.c so that the code implementing
the private screenshooter protocol and launching the client is
moved to a weston specific file, leaving only the code that can
be shared between compositors in screenshooter.c.
Two exported functions are added in screenshooter.c to start and
stop the recorder.

Signed-off-by: Giulio Camuffo <giuliocamuffo@gmail.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

desktop-shell/shell.c

@@ -36,6 +36,7 @@
 #include <sys/types.h>
 
 #include "shell.h"
+#include "weston.h"
 #include "weston-desktop-shell-server-protocol.h"
 #include "shared/config-parser.h"
 #include "shared/helpers.h"