added UrlShortner.Tests project; created AutoMapperConfigurationTests
deleted UrlModel class; no longer in use
remoted UrlModel; implemented some helper methods in view model classes for display timestamps
created DateTimeOffsetExtensions class; updated UrlDetailsViewModel and NewShortLink to use DateTimeOffset.ToFriendlyString()
modified UrlIndexViewModel to use ShortLinkDetails view model instead of ShortLink; modifed Url\Index view to use new timestamp helper methods; implemented ConfigurationHelper;