Add support for potion effect upgrades in Upgrade Waves.

It doesn't seem like there was any real reason to leave out potion effects as upgrades in Upgrade Waves previously, so they were likely just forgotten in the Things API overhaul.

Closes #565

src/main/java/com/garbagemule/MobArena/waves/WaveParser.java

@@ -542,6 +542,26 @@ public class WaveParser
             throw new ConfigError("Failed to parse armor upgrades for class " + className + " in wave " + name + " of arena " + arena.configName() + ": " + e.getInput());
         }
 
+        // Effects
+        List<String> effects = classSection.getStringList("effects");
+        if (effects == null || effects.isEmpty()) {
+            String value = classSection.getString("effects", null);
+            if (value == null || value.isEmpty()) {
+                effects = Collections.emptyList();
+            } else {
+                effects = Arrays.asList(value.split(","));
+            }
+        }
+        try {
+            // Prepend "effect:" for the potion effect thing parser
+            effects.stream()
+                .map(String::trim)
+                .map(s -> thingman.parse("effect", s))
+                .forEach(list::add);
+        } catch (InvalidThingInputString e) {
+            throw new ConfigError("Failed to parse potion effects for class " + className + " in wave " + name + " of arena " + arena.configName() + ": " + e.getInput());
+        }
+
         try {
             // Prepend "perm:" for the permission thing parser
             classSection.getStringList("permissions").stream()