perf ui: Start breaking down newt.c into multiple files

As new TUI features get added the newt.c file is growing a lot and its
name is growing misleading as an effort is being made to reduce the
coupling with libnewt.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>