Implement decompilation

[alexrp]

Ideally, we'd use ICSharpCode.Decompiler if/when it's separated into its own Git repository.

[alexrp]

Now available as a NuGet package: https://www.nuget.org/packages/ICSharpCode.Decompiler

Should be fairly trivial to implement now. Though we should probably move SDB to the new .NET SDK style project format before using any NuGet packages.