Steam Guard support

[iTaysonLab]

This is a mega-issue describing parts which we need to implement to get Steam Guard support fully working

V1:

• [X] Generating TOTP codes
• [X] Adding a new authenticator if none are present
• [X] Removing authenticator
• [X] Recovery code display
• [X] Trading confirmations

V2:

• [X] Moving authenticator from other devices
• [X] "Authorized Devices": session list
• [X] "Authorized Devices": dedicated session page with revoke options
• [X] Mobile Confirmation: polling for new auth sessions
• [X] Mobile Confirmation: confirmation UI and actually signing in
• [X] Sign in using QR

Custom (not related to official app parity:)

• [ ] .mafile support (export/import): requires multi account supported

V1, but won't be implemented:

• Home screen widget: Glance is not ready yet + no need for it

V2, but won't be implemented:

• Pushes: needs FCM
• Google Maps in Mobile Confirmation UI: needs FCM and Maps SDK
• Multi-account support: needs global rework of application's session handling

[muznyo]

also import otp token from bitwarden could be nice https://bitwarden.com/help/authenticator-keys/#steam-guard-totps