LegalScreen: Turn into a global, all-accounts screen

[chrisbobbe]

The user should be equally aware of the terms for all realms the app is interacting with, and that includes realms other than the active account's realm. (There would be even more interaction in a future with better multi-account support.)

Rather than make the user traverse all realms with the "active account" pointer to find all the relevant terms, it seems nicer to show them together on this one page.

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Also, for #4729, if we still want the "Legal" link to live in a settings menu, then we'll want to choose whether the "Legal" screen is per-account or global, and it seems more global to me.

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(The "After" screenshot shows an IP address as a realm. It's a valid realm—my dev server—but most people won't see ugly numbers like that.)

Before	After