Extend Velopack.Build to support enhanced debugging

[caesay]

The Velopack.Build project provides msbuild integration, and it would be sweet if it was capable of modifying the build output to emit important files and folder structure (like Update.exe, sq.version, etc) so that the resulting app could be debugged by visual studio.

This diagnostics mode should default to ON in debug configuration, and OFF in release configuration, but can be overridden in the csproj.

The 3 things required for debugging to work is:

• build output created in a {build}\current sub-folder.
• Update.exe copied to {build}\Update.exe.
• {build}\current\sq.version manifest created containing product name, version etc.