Improve TOTP autocomplete behaviour

[squaredpx]

Hi! This is a little improvement over #373 that included the autocomplete attribute. I've set it attribute to 'one-time-code' so browsers and password managers can autocomplete the code if necessary/possible. I've tested it on the latest versions of 1Password and Safari, Chrome, Firefox & Edge and it autocompletes the TOTP code (previously it only worked on Safari)

Great job with the plugin by the way, thanks!

[jeffpaul]

Per yesterday's bug scrub, we're punting this to a future release so we can focus on the U2F deprecation in 0.8.0.

[kasparsd]

This is great UX improvement and a minimal change so we can merge this in and adjust if necessary based on user feedback.