perf hists browser: Display columns header text on 'H' press

Displaying columns header text whenever 'H' is pressed,
and hiding it on on another press.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-w9pcqpum5erza2a05ysvollz@git.kernel.org


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