Replace the Fetcher by Container and refactor media type sniffing

[mickael-menu]

Changelog

Changed

Shared

• Publication.localizedTitle is nullable, as we cannot guarantee that all publication sources offer a title.
• The MediaType sniffing helpers are deprecated in favor of MediaTypeRetriever (for media type and file extension hints and raw content) and AssetRetriever (for URLs).

Streamer

• The Fetcher interface was deprecated in favor of the Container one in readium-shared.

Notes

• Href API was revamped and now supports file:// schemes.
• Removed Asset.name, Container.name and Resource.name.