perf, sched migration: Make the GUI class client agnostic

Make the perf migration GUI generic so that it can be reused for
other kinds of trace painting. No more notion of CPUs or runqueue
from the GUI class, it's now used as a library by the trace parser.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Nikhil Rao <ncrao@google.com>
Cc: Tom Zanussi <tzanussi@gmail.com>