Metadata enhancer to enrich resources and extraction of metadata guessing

[ElectricMaxxx]

When working on resources i realized, that the work of this bundle could also enrich resource data. So i would propose an enhancer that would do that.

From the responsibility view i would suggest the complete guessing and metadata collection function in a kind of MetadataBundle/Component. So other components/bundles can use it without have the conflict to require a SeoBundle. Use cases can be:

• enhancer for resource data
• FosHttpCache (especially the [Sitemap] Provide default last modification date guesser #292)
• SeoBundle itself