Changed activity creation logic

- for home activity it will reuse existing activity from back stack and
  also clears all current activities
- for nearby, about and settings, it will use the existing activity from
  back stack

app/src/main/java/fr/free/nrw/commons/auth/LoginActivity.java

@@ -30,6 +30,7 @@ import fr.free.nrw.commons.R;
 import fr.free.nrw.commons.Utils;
 import fr.free.nrw.commons.WelcomeActivity;
 import fr.free.nrw.commons.contributions.ContributionsActivity;
+import fr.free.nrw.commons.theme.NavigationBaseActivity;
 import timber.log.Timber;
 
 import static android.view.KeyEvent.KEYCODE_ENTER;
@@ -176,7 +177,7 @@ public class LoginActivity extends AccountAuthenticatorActivity {
     }
 
     public void startMainActivity() {
-        ContributionsActivity.startYourself(this);
+        NavigationBaseActivity.startActivityWithFlags(this, ContributionsActivity.class, Intent.FLAG_ACTIVITY_CLEAR_TOP);
         finish();
     }