Move ArchiveReaders to a more global namespace

Also moves delete and action logic to a shared implementation

osu.Game/IO/Archives/ArchiveReader.cs

@@ -0,0 +1,47 @@
+// Copyright (c) 2007-2018 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using osu.Framework.IO.Stores;
+
+namespace osu.Game.IO.Archives
+{
+    public abstract class ArchiveReader : IDisposable, IResourceStore<byte[]>
+    {
+        /// <summary>
+        /// Opens a stream for reading a specific file from this archive.
+        /// </summary>
+        public abstract Stream GetStream(string name);
+
+        public abstract void Dispose();
+
+        /// <summary>
+        /// The name of this archive (usually the containing filename).
+        /// </summary>
+        public readonly string Name;
+
+        protected ArchiveReader(string name)
+        {
+            Name = name;
+        }
+
+        public abstract IEnumerable<string> Filenames { get; }
+
+        public virtual byte[] Get(string name)
+        {
+            using (Stream input = GetStream(name))
+            {
+                if (input == null)
+                    return null;
+
+                byte[] buffer = new byte[input.Length];
+                input.Read(buffer, 0, buffer.Length);
+                return buffer;
+            }
+        }
+
+        public abstract Stream GetUnderlyingStream();
+    }
+}