Provide additional runtime information through helper files

[csoltenborn]

GTA does not have information to certain runtime information if run as NuGet package, e.g. placeholders $(PlatformName), $(ConfigurationName), and $(SolutionDir) are not available. Additionally, VS project configuration is not available.

Both drawbacks can be tackled by providing a notion of helper files, which are written as part of building the project (e.g.m as part of a post-build step) and make that information available to GTA.