lisa.analysis.tasks: Fix histograms
lisa.analysis.tasks: Fix histograms

* Keep accurate timestamps at window boundaries by using df_window() instead of
  df_refit_index(), since we are interested in transitions rather than a
  "continuous" signal.

* Fix histogram plotting with matplotlib by passing numpy arrays instead of
  pandas Series.

* Remove local_fig parameter that is unused when
  TraceAnalysisBase.plot_method(return_axis=True) is used.

credp/lisa,ARM-software/lisa,ARM-software/lisa,ARM-software/lisa,credp/lisa,ARM-software/lisa,credp/lisa,credp/lisa