Fix various hints and warnings on many set & block classes (via IntelliJ IDEA linting):

- replacing hard coded strings of set codes with reference to 'mage.sets.<set>.getInstance().getCode()' allows for set class names to no longer show as unreferenced & adds for more consistence between other block units
- various protected variables were able to be changed to private to clean up additional warnings
- some JavaDoc comments were generating warnings due to missing documentation
- removed some unused imports and unused variables
- there were multiple conditional logic checks for 'rarity != Rarity.LAND' within an if block where the outer condition was 'if rarity == Rarity.COMMON' rendering the inner condition always true and thus redundant
- a few ExpansionSet.buildDate parameters wer using octal values (eg. '03' instead of '3') which triggered some warnings
- added a booster generation test for WarOfTheSparks to make sure every booster contains a planeswalker
- added a booster generation test for ModernHorizons to make sure every booster contains a snow land
- booster generation test for Battlbond set referenced the Coldsnap set class instead of Battlebond

Mage.Sets/src/mage/sets/AetherRevolt.java

@@ -22,7 +22,7 @@ public final class AetherRevolt extends ExpansionSet {
         return instance;
     }
 
-    protected final List<CardInfo> savedSpecialLand = new ArrayList<>();
+    private final List<CardInfo> savedSpecialLand = new ArrayList<>();
 
     private AetherRevolt() {
         super("Aether Revolt", "AER", ExpansionSet.buildDate(2017, 1, 20), SetType.EXPANSION);