improve relay section fo the FAQ
context: https://lists.torproject.org/pipermail/tor-relays/2018-February/014471.html
find the updates in my branch on gh: https://github.com/nusenu/torproject-webwml/tree/FAQ_relay_section_improvements
FAQ (relay section): new entry: Can I used IPv6 on my relay?
FAQ (relay section): link to new relay guide; link to obfs4 bridge guide
FAQ (relay section): move two questions out of the relay section
FAQ (relay section): update BadExit question (wiki is obsolete, add email address)
FAQ (relay section): refrase static IP section into a question
FAQ (relay section): NAT is covered in its own section (this section is about stability)
FAQ (relay section): bw shaping is covered in its own section (this section is about stability)
FAQ (relay section): put most relevant answer in this question at the beginning
FAQ (relay section): dynamic IPs are covered in a dedicated answer already
FAQ (relay section): new entry: most wanted relay type
FAQ (relay section): increase min. bw from 2 to 8 MBit/s and add bridge info