When developing Dokku, it is useful to use a real domain to test actual functionality. This is impossible if the domain is hardcoded to dokku.me in testing.
This change makes interacting with port mappings more clear - folks might previously set the port mapping to the proxy type or vice-versa.
The existing proxy:ports* commands still exist but will show a deprecation warning for a single minor release.
This makes the installation a bit more secure by ensuring a user does not accidentally expose a way for unauthorized users to add new ssh keys to the system.
Additionally, this removes the extra HOSTNAME file to make the initial install process easier (that file was not modifiable by any dokku commands.
Closes#2247
