add: added .rakeback to get a part of the house edge back. Rakeback is accumulated by betting (not winning or losing in particular). All games have manually specified rakeback values

add: slot now has 1 more icon (wheat!), and multipliers have been modified to even out the gains
change: betroll is improved (around 2% better payout), as 66 is now a winning number, not a losing one

src/NadekoBot/Migrations/Sqlite/20241105072953_rakeback.cs

@@ -0,0 +1,34 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace NadekoBot.Migrations
+{
+    /// <inheritdoc />
+    public partial class rakeback : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.CreateTable(
+                name: "Rakeback",
+                columns: table => new
+                {
+                    UserId = table.Column<ulong>(type: "INTEGER", nullable: false)
+                        .Annotation("Sqlite:Autoincrement", true),
+                    Amount = table.Column<decimal>(type: "TEXT", nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_Rakeback", x => x.UserId);
+                });
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropTable(
+                name: "Rakeback");
+        }
+    }
+}