Migrate default configs from INI to JSON

[eyedeekay]

Preserve compatibility with INI config by translating from INI config files to JSON config files on the fly, but some way or another get rid of the goddawful INI business I did on top of /config and replace it with something Go-native and sane(JSON). Config files will work basically the same, with defaults at the top level and tunnel-specific settings specified underneath.