Support quickly switching between multiple accounts

[luaneko]

Suggested by UnkWeil#9701 on Discord

Is it possible to have an option to add more resin calculators? Because I have 2 accounts and i'm sure a lot of people also have 2 account or more. And also, to be able to give names to our different calculators.

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Due to the way resin calculators are implemented right now, it's not easy to make a "multiple calculator" feature. I think a better way to approach this would be to make a quick account switcher that lets you sign in to another account without having to type in the username/password, similar to how Google does it.