remove calls to private functions in other classes

[rpoleski]

In event.py we're calling:

MulensData._plot_datapoints() MulensData._set_plot_properties()

which should not be done. Maybe there are other similar cases to correct.

[rpoleski]

The only other problematic case is:

• fitdata.py -> self.model._parallax

[rpoleski]

The last one is solved in cb303e4. First two issues remain.