[feature request] Add access restrictions per device

**Motivation**
When logged into keybase, sometimes you dont want certain devices to have access to all of your data.

**Feature request**
Allow each chat room, team, git repo, wallet, and folder to have read access permissions for each verified device.

**Use cases**
* On my cell phone, i might only like to have acces to certain chat rooms, but not all of my highy sensitive files.
* On my work computer, i might not want to have acces to private chat rooms with my friends, nor folders with personal files.
* When I take my laptop on vacation, I might want to temporarily restrict access to certain highly sensitive conversations, files, or wallet.

The issue names no files, tests, or entry points; begin by mapping how Keybase authorizes access to chat rooms, teams, git repos, wallets, and folders across verified devices. Define the device-level permission model and its behavior before implementation, then verify restrictions for each requested resource and temporary access changes.

Written by the indexing model from the issue text.