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/PostgreSql/20241105073004_rakeback.cs

@@ -0,0 +1,33 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace NadekoBot.Migrations.PostgreSql
+{
+    /// <inheritdoc />
+    public partial class rakeback : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.CreateTable(
+                name: "rakeback",
+                columns: table => new
+                {
+                    userid = table.Column<decimal>(type: "numeric(20,0)", nullable: false),
+                    amount = table.Column<decimal>(type: "numeric", nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("pk_rakeback", x => x.userid);
+                });
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropTable(
+                name: "rakeback");
+        }
+    }
+}