Cleaned up some unused/commented code

- Small amount of refactoring
- Separated imagesharp extension to ImageSharpExtensions.cs
- Using .join Ienumerable extension instead of string.join in some places

src/NadekoBot/Modules/Gambling/~Shared/Decks/QuadDeck.cs

@@ -0,0 +1,17 @@
+namespace NadekoBot.Modules.Gambling.Common;
+
+public class QuadDeck : Deck
+{
+    protected override void RefillPool()
+    {
+        CardPool = new(52 * 4);
+        for (var j = 1; j < 14; j++)
+        for (var i = 1; i < 5; i++)
+        {
+            CardPool.Add(new((CardSuit)i, j));
+            CardPool.Add(new((CardSuit)i, j));
+            CardPool.Add(new((CardSuit)i, j));
+            CardPool.Add(new((CardSuit)i, j));
+        }
+    }
+}