Server: Improve 2FA selection screen

[rullzer]

Our current 2FA selection screen (if you have multiple providers). Looks like:

Which is not to pretty IMO.

Something like (excuse my awesome artistic skills):

Would be nicer I think.
Tiles with a description would also be 'easy' (for somebody with CSS knowledge) to make responsive for the mobile UI.

@nextcloud/designers
@ChristophWurst as it is 2FA stuff ;)

[nextcloud-bot]

GitMate.io thinks possibly related issues are https://github.com/nextcloud/server/issues/1120 (2FA: skip selection screen if there's only one active provider for the user), https://github.com/nextcloud/server/issues/7018 (Backlink to 2FA selection), https://github.com/nextcloud/server/issues/6672 (Dedicated favicon selection), https://github.com/nextcloud/server/issues/9441 (Improve token handling), and https://github.com/nextcloud/server/issues/9113 (Improve loginflow text).

[skjnldsv]

I'm not fond of the "blah blah" text, can we change? :thinking:

Nice improvements btw ;)

[jancborchardt]

As discussed with @rullzer & @ChristophWurst – Christoph will create a branch with all that’s needed for the screen and I’ll do the layout. :)