Add default app logic to hosting extension package

[dasMulli]

As a follow-up to #57, #58:

investiate how much of the samples can potentially be moved to the hosting extension NuGet package. And possibly the main package.

Since users have in most cases copied the sample projects or used https://github.com/PeterKottas/DotNetCore.WindowsService, there may be some potential to create a highly opinionated application model based on the sample code.

[dasMulli]

Leaving this out for now since it don't have a good plan at the moment. Peter Kottas has a nice wrapper already.. https://github.com/PeterKottas/DotNetCore.WindowsService