Crash when recreating MainActivity

[macgills]

Summary:

ContributonListFragment does not have an empty constructor because of this

  ContributionsListFragment(final Callback callback) {
    this.callback = callback;
  }

The code must be rewritten to not pass the callback into the constructor.

Steps to reproduce:

Turn on "don't keep activities"
rotate device on main screen

System logs:

Caused by: androidx.fragment.app.Fragment$InstantiationException: Unable to instantiate fragment fr.free.nrw.commons.contributions.ContributionsListFragment: could not find Fragment constructor

Commons app version:

master