✨ Adds HOTP MFA code support

[nefrob]

Adds support for counter based 2fa codes for all 2fa methods except app/yubi key

Ref merixstudio#206. It's been 5+ months since this was written so I'm pulling it into our fork.

Please note this repo is currently public so keep your comments non-Tilt specific. Alternatively @roycehaynes transition the repo to being private.

Description

• HOTP codes are guaranteed to be unique by incrementing a counter each time a code is generated
• Consequently generating a new code invalidates the previously generated code
• Storing a timestamp on code generation allows us to use validity windows
• Clearing the timestamp on successful verify invalidates the current code so it can't be used again
• To switch to HOTP based codes simply override the default message dispatcher used in the trench settings

Motivation

• Have SMS MFA codes cycle every generation
• Keep the security benefits of TOTP