add more mechanisms in support of correct xp modifier in tutorial

- Adds lines `experience_modifier=100` to both tutorial scenarios
- When writing a saved_game, write the mp game settings (including
  the experience modifier setting) for TEST and TUTORIAL scenario
  types as well.

There are no "test campaigns" right now, so this won't be a
problem.

data/campaigns/tutorial/scenarios/01_Tutorial_part_1.cfg

@@ -11,6 +11,7 @@
     turns=12
     next_scenario=2_Tutorial
     victory_when_enemies_defeated=no
+    experience_modifier=100
 
     {DEFAULT_SCHEDULE}
 

data/campaigns/tutorial/scenarios/02_Tutorial_part_2.cfg

@@ -5,6 +5,7 @@
     name= _ "Wesnoth Tutorial — Part II"
     map_data="{campaigns/tutorial/maps/02_Tutorial_part_2.map}"
     turns=26
+    experience_modifier=100
 
     {DEFAULT_SCHEDULE}
 

src/saved_game.cpp

@@ -145,10 +145,7 @@ void saved_game::write_carryover(config_writer& out) const
 void saved_game::write_general_info(config_writer& out) const
 {
 	out.write(classification_.to_config());
-	if (classification_.campaign_type == game_classification::MULTIPLAYER
-			|| classification_.campaign_type == game_classification::SCENARIO) {
-		out.write_child("multiplayer", mp_settings_.to_config());
-	}
+	out.write_child("multiplayer", mp_settings_.to_config());
 }