Better login and unlock handling

[Yamakaky]

Currently, the script asks the user for his password for login and unlock. This breaks the TOTP login workflow, and maybe other ones like SSO?

A better way would be to directly expose the bw interface. With --raw, stderr shows ? Master password: [input is hidden] and such, and stdout shows the session key. That way, the script only has to capture stdout, with stdin and stderr set as inherit.