Move ArchiveReaders to a more global namespace

Also moves delete and action logic to a shared implementation

osu.Game/Database/MutableDatabaseBackedStore.cs

@@ -0,0 +1,76 @@
+using System;
+using osu.Framework.Platform;
+
+namespace osu.Game.Database
+{
+    /// <summary>
+    /// A typed store which supports basic addition, deletion and updating for soft-deletable models.
+    /// </summary>
+    /// <typeparam name="T">The databased model.</typeparam>
+    public abstract class MutableDatabaseBackedStore<T> : DatabaseBackedStore
+        where T : class, IHasPrimaryKey, ISoftDelete
+    {
+        public event Action<T> ItemAdded;
+        public event Action<T> ItemRemoved;
+
+        protected MutableDatabaseBackedStore(IDatabaseContextFactory contextFactory, Storage storage = null)
+            : base(contextFactory, storage)
+        {
+        }
+
+        public void Add(T item)
+        {
+            using (var usage = ContextFactory.GetForWrite())
+            {
+                var context = usage.Context;
+                context.Attach(item);
+            }
+
+            ItemAdded?.Invoke(item);
+        }
+
+        /// <summary>
+        /// Update a <see cref="T"/> in the database.
+        /// </summary>
+        /// <param name="item">The item to update.</param>
+        public void Update(T item)
+        {
+            ItemRemoved?.Invoke(item);
+
+            using (var usage = ContextFactory.GetForWrite())
+                usage.Context.Update(item);
+
+            ItemAdded?.Invoke(item);
+        }
+
+        public bool Delete(T item)
+        {
+            using (ContextFactory.GetForWrite())
+            {
+                Refresh(ref item);
+
+                if (item.DeletePending) return false;
+
+                item.DeletePending = true;
+            }
+
+            ItemRemoved?.Invoke(item);
+            return true;
+        }
+
+        public bool Undelete(T item)
+        {
+            using (ContextFactory.GetForWrite())
+            {
+                Refresh(ref item);
+
+                if (!item.DeletePending) return false;
+
+                item.DeletePending = false;
+            }
+
+            ItemAdded?.Invoke(item);
+            return true;
+        }
+    }
+}