Support "structured syntax suffix"/"fragid"s in media type providers

Mimetypes can contain a "structured syntax suffix" (SSS, specified in RFC6838 section 4.2.8). For example "application/vnd.custom+json", should be regarded as "application/json".

Currently, providers are returned that are strictly compatible with a requested mimetype, meaning that for "application/vnd.custom+json" only a provider with that particular mimetype is to be returned. While that works, it should also be possible to let a provider registered for "application/json" to be returned. This would make it easier for "vendor specific mimetypes" based on JSON to use the generic JSON provider.

I've worked out a patch for Wink already, but want to give it some additional testing. When this is done, I'll attach it to this issue...