SC2: Greater variety on short generations (#1367)

Originally, short generations used an artificial cull to create balanced mission distributions. This resulted in campaigns that were somewhat too consistent, and on some standard settings combinations, this resulted in campaigns having The Outlaws as the second mission 100% of the time. It also caused generation to fail a bit too easily if the player excluded too many missions.

This removes the cull and adds an additional early Easy mission slot to all of the reduced sized campaigns.

When playing on No Build settings, this also pushes many of the missions down a difficulty level to ensure greater variety, and pushes additional missions down on Advanced Tactics.

Additional small fixes:

The in-world Excluded Missions validation check is replaced by the core OptionSet check.
Fixed issue with Existing Items not getting their upgrades locked with Units Always Have Upgrades on.

Starcraft2Client.py

@@ -52,9 +52,9 @@ class StarcraftClientProcessor(ClientCommandProcessor):
         """Overrides the current difficulty set for the seed.  Takes the argument casual, normal, hard, or brutal"""
         options = difficulty.split()
         num_options = len(options)
-        difficulty_choice = options[0].lower()
 
         if num_options > 0:
+            difficulty_choice = options[0].lower()
             if difficulty_choice == "casual":
                 self.ctx.difficulty_override = 0
             elif difficulty_choice == "normal":
@@ -71,7 +71,11 @@ class StarcraftClientProcessor(ClientCommandProcessor):
             return True
 
         else:
-            self.output("Difficulty needs to be specified in the command.")
+            if self.ctx.difficulty == -1:
+                self.output("Please connect to a seed before checking difficulty.")
+            else:
+                self.output("Current difficulty: " + ["Casual", "Normal", "Hard", "Brutal"][self.ctx.difficulty])
+            self.output("To change the difficulty, add the name of the difficulty after the command.")
             return False
 
     def _cmd_disable_mission_check(self) -> bool: