Feature/langloc

This will return a client.json file based on user preference.
It will work from most preferred to least, to "en" as the default.
It also presumes all pathnames are in lower case (because LCD)

@kitcambridge, @nchapman r?
I think this could be simplified to `r >= '0' && r <= '9' || r >= 'A' && r <= 'Z' || r >= 'a' && r <= 'z' || r == '.' || r == '-' || r == ';' || r == ','`—avoids the `unicode` table machinery.