Delete data_file parameter from plot_mf_coupled()

- Also add plot styling parameters to this method.
Modify plot_time_series_normalized()

- Add plotting parameters to the method.
Remove 'data_file' from plot_mf_minimal_coupled()
Modify plot_mf_minimal_coupled()

- Add plotting parameters to the method.
Adjust plot_mf_minimal_coupled()

- Consider the sequence of events in order to adjust the equations.
Adjust plot_mf_coupled()

- During the "Death of preys" stage, the density of preys that die is
  equal to the density of predators in the previous stage.
Adjust plot_mf_coupled_phase()

- During the "Death of preys" stage, the density of preys that die is
  equal to the density of predators that survived the "Death of
  predators stage".