perf ui/gtk: Add GTK statusbar widget to browser window

Add statusbar widget to display non-critical messages at the bottom of
the window. This can be used for showing a status change, warning or
help message.

Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Acked-by: Pekka Enberg <penberg@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1338265382-6872-6-git-send-email-namhyung@gmail.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>