IP matching refactor, allow Docker, explanatory error messages

1. allow requests from the 172.*.*.* range - so that the app server can be run in a Docker container and accessed from the host
2. correct local ip regex from . (any char) to literal '.' (\.)
3. refactor host matching because there's now more of them
4. use remote address for request filtering (rather than the local one) - so that we can demo the filtering from e.g. a phone (this only applies to dockerized or otherwise isolated app servers)
5. show more explanatory unsuccessful filter responses - so that the client can actually tell what's wrong