Web-based initial setup

[eartharoid]

https://christmascountdown.live/discord/add could have a form that asks

• which countdowns and features to enable
• server timezone (international or local)
• user timezone (suggest from browser)
• Configurable countdown target? #85

Then

1. Store answers in local storage? or submit the form to the bot
2. Create webhook with OAuth2 #79
3. After callback, apply settings.

Also, have a similar wizard for /setup?