WIP (do not merge!)- Type relative URIs, Template relative URIs

Making template and CSS URIs relative to the library in which the type which is annotated resides. This resolves the template and CSS URIs against the type's location.

Also this leverages some code from Polymer to make the loaded HTML contents and CSS be relative to those files.

The two changes are separable, but I think it makes sense to at least discuss in parallel:

 - Annotation URIs are relative to the type which is being annotated.
 - URIs within templates and CSS are relative to those files.

Primary work remaining- support for the static case.