Add back osu.Desktop project

While it was nice having less projects to deal with, it meant hacks to get around circular dependencies between rulesets and osu.Game. For now, let's just restore the osu.Desktop project and call it a day.

This allows for the project to build again with default visual studio settings.

osu.Desktop/Properties/AssemblyInfo.cs

@@ -0,0 +1,28 @@
+// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using System.Reflection;
+using System.Runtime.InteropServices;
+
+// General Information about an assembly is controlled through the following
+// set of attributes. Change these attribute values to modify the information
+// associated with an assembly.
+[assembly: AssemblyTitle("osu!lazer")]
+[assembly: AssemblyDescription("click the circles. to the beat.")]
+[assembly: AssemblyConfiguration("")]
+[assembly: AssemblyCompany("ppy Pty Ltd")]
+[assembly: AssemblyProduct("osu!lazer")]
+[assembly: AssemblyCopyright("ppy Pty Ltd 2007-2017")]
+[assembly: AssemblyTrademark("")]
+[assembly: AssemblyCulture("")]
+
+// Setting ComVisible to false makes the types in this assembly not visible
+// to COM components.  If you need to access a type in this assembly from
+// COM, set the ComVisible attribute to true on that type.
+[assembly: ComVisible(false)]
+
+// The following GUID is for the ID of the typelib if this project is exposed to COM
+[assembly: Guid("55e28cb2-7b6c-4595-8dcc-9871d8aad7e9")]
+
+[assembly: AssemblyVersion("0.0.0")]
+[assembly: AssemblyFileVersion("0.0.0")]