Revert "Remove all EF migrations"

This reverts commit bb5b9458e8.

osu.Game/Migrations/20190525060824_SkinSettings.cs

@@ -0,0 +1,54 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+namespace osu.Game.Migrations
+{
+    public partial class SkinSettings : Migration
+    {
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.Sql(@"create table Settings_dg_tmp
+            (
+	            ID INTEGER not null
+		            constraint PK_Settings
+			            primary key autoincrement,
+	            Key TEXT not null,
+	            RulesetID INTEGER,
+	            Value TEXT,
+	            Variant INTEGER,
+	            SkinInfoID int
+		            constraint Settings_SkinInfo_ID_fk
+			            references SkinInfo
+				            on delete restrict
+            );
+
+            insert into Settings_dg_tmp(ID, Key, RulesetID, Value, Variant) select ID, Key, RulesetID, Value, Variant from Settings;
+
+            drop table Settings;
+
+            alter table Settings_dg_tmp rename to Settings;
+
+            create index IX_Settings_RulesetID_Variant
+	            on Settings (RulesetID, Variant);
+
+            create index Settings_SkinInfoID_index
+	            on Settings (SkinInfoID);
+
+            ");
+        }
+
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropForeignKey(
+                name: "FK_Settings_SkinInfo_SkinInfoID",
+                table: "Settings");
+
+            migrationBuilder.DropIndex(
+                name: "IX_Settings_SkinInfoID",
+                table: "Settings");
+
+            migrationBuilder.DropColumn(
+                name: "SkinInfoID",
+                table: "Settings");
+        }
+    }
+}