Support disabling fallback to html document title

[CedricReichenbach]

If a website doesn't support oEmbed, this library falls back to document title and some meta tags (e.g. for description) instead of just leaving them null. This is problematic when other meta data sources (like OpenGraph) besides oEmbed, since getTitle() will always return a non-null value.

My current workaround is to check getVersion() as indicator whether data was fetched from an actual oEmbed endpoint, but that's quite hacky. It would be nice to have an option to disable default behavrior, e.g. through an argument like boolean useMetaTagFallbacks in the constructor of DefaultOEmbedProvider.