Improve support for embedded resources and NuGet it up

This PR seeks to put embedded content on the SDHP by fixing a remaining issue and closing out #732.

## Questions i have

1. ~~Should i move everything related to embedded views out of core Nancy and into Nancy.Embedded?~~
1. ~~When wiring up embedded views for Nancy, i followed [this post](http://simoncropp.com/embeddingviewsasresourcesinnancyfx) by Simon Cropp. It was pretty simple, but according to #732 it sounds like @grumpydev had some ideas on how to improve wiring up embedded views. Is there a better way to wire up embedded views?~~

## Done
* [x] Fix issue with embedded views in an outside assembly mentioned in [this mailing list post](http://groups.google.com/d/msg/nancy-web-framework/9N4f6-Y4dNA/ZcGu35SBMoYJ). Thanks for the fix, Rex!
* [x] Add an extension that allows an `AddDirectory` for embedded static content, similar to the extension method on the default `StaticContentConventions`
* [x] Wire up embedded views via an `ApplicationRegistration`
* [x] Figure out the best way to handle issue with no `RootNamespaces` added and only one embedded view to serve.