Before this change, rclone ignored the --password-command on the
rclone config setting except when decrypting an existing config file.
This change allows for offloading the password storage/generation into
external hardware key or other protected password storage.
Fixes#7859
This splits config.go into ui.go for the user interface functions and
authorize.go for the implementation of `rclone authorize`.
It also moves the tests into the correct places (including one from
obscure which was in the wrong place).