MMVM Light + Clean up

Introduced "MMVM light toolkit" (https://mvvmlight.codeplex.com/) as
framework for the application. The application was already following the
same structure as an MVVM light application, so only small changes were
done.
Removed "Packages" folder from repository, enabled "NuGet Package
Restore" for solution.
Updated Costura.Fody from 1.1.0.0 to 1.2.0.0