Addin: Change project file to open in every VS version

Still requires the appropriate SDK to be installed.
Thanks @sharwell for much simpler implementation

ILSpy.AddIn/ILSpy.AddIn.csproj

@@ -1,9 +1,13 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003" ToolsVersion="12.0">
   <PropertyGroup>
-    <MinimumVisualStudioVersion>12.0</MinimumVisualStudioVersion>
-    <VisualStudioVersion Condition="'$(VisualStudioVersion)' == ''">12.0</VisualStudioVersion>
-    <VSToolsPath Condition="'$(VSToolsPath)' == ''">$(MSBuildExtensionsPath32)\Microsoft\VisualStudio\v$(VisualStudioVersion)</VSToolsPath>
+    <!-- Use the SDK for the current version of Visual Studio -->
+    <VsSdkTargets Condition="'$(VisualStudioVersion)'!=''">$(MSBuildExtensionsPath)\Microsoft\VisualStudio\v$(VisualStudioVersion)\VSSDK\Microsoft.VsSDK.targets</VsSdkTargets>
+    <VsSdkTargets Condition="'$(VisualStudioVersion)'==''">$(MSBuildExtensionsPath)\Microsoft\VisualStudio\v10.0\VSSDK\Microsoft.VsSDK.targets</VsSdkTargets>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(VisualStudioVersion)' != ''">
+    <!-- This is added to prevent forced migrations in Visual Studio 2012 and newer -->
+    <MinimumVisualStudioVersion>$(VisualStudioVersion)</MinimumVisualStudioVersion>
   </PropertyGroup>
   <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
   <PropertyGroup>
@@ -20,6 +24,12 @@
     <AssemblyOriginatorKeyFile>Key.snk</AssemblyOriginatorKeyFile>
     <TargetFrameworkVersion>v4.5</TargetFrameworkVersion>
   </PropertyGroup>
+  <PropertyGroup>
+    <!-- Common debugging support -->
+    <StartAction>Program</StartAction>
+    <StartProgram>$(DevEnvDir)\devenv.exe</StartProgram>
+    <StartArguments>/rootSuffix Exp</StartArguments>
+  </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>
     <DebugType>full</DebugType>
@@ -187,7 +197,7 @@
     <UseCodebase>true</UseCodebase>
   </PropertyGroup>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
-  <Import Project="$(VSToolsPath)\VSSDK\Microsoft.VsSDK.targets" Condition="'$(VSToolsPath)' != ''" />
+  <Import Condition="Exists($(VsSdkTargets))" Project="$(VsSdkTargets)" />
   <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
        Other similar extension points exist, see Microsoft.Common.targets.
   <Target Name="BeforeBuild">