Previously we were using names "Knot DNS Resolver" and "Knot Resolver"
interchangibly and the prefix "Knot DNS" was somehow confusing users.
Let's see if this rebranding actually helps or not.

- no need to have gitter twice
- update information about modules (one cache, no alternative backends)
- add EPEL 7
- add mailing-list
- link to stable docs instead of latest master

Homepage link was broken – https://www.knot-resolver.cz/pages/try.html returns 404 (moved to /download during website redesign)

Updated Docker run command, because without -it (interactive) switch, kresd would freeze upon startup on [system] interactive mode. That may as well be a defect, but adding -it helps in all cases.
Also updated the URL to the correct address (you'd get redirected automatically, but still).

also some cleanup and version bump to Q2