Strong Content-Type validation

[krizhanovsky]

Content-Type is important HTTP header with large security implication, so __parse_content_type() must be enhanced to check the RFC values for the header. Frang http_ct_vals limit must be moved to HTTP parser. BG algorithm must be used for multi-pattern matching. The multi-pattern matching must be done in generic way, so it depends on #732. Also consider its implementation in Linux kernel to be applicable for nftables (mainstream patch is appriciated).

We also should implemente Content-Type validation against resource type requested in URI, see CloudFlare's feature in AppSecCali 2019 - Cache Me If You Can: Messing with Web Caching

Also please update Web security and Frang Wikis and create a new functional test issue for the next milestone.