perf gtk/annotate: Support multiple event annotation

Show multiple annotation result for each evsel.  Each result represents
the most frquently sampled symbol/function for the evsel and it will be
shown in a tab window.

For this add a reference to main container (notebook) to the pgctx.  At
the first call to annotate browser, hist_entry__find_annotations() will
setup a new browser, and next calls will add new tabs to the browser.
But it requires final perf_gtk__show_annotations() to start processing
GUI events.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
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/1360227734-375-3-git-send-email-namhyung@kernel.org


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