Issue title: Multi-device management
 Issue body: We need to decide how we want to manage multiple devices (e.g. Desktop, laptop, cloud VM).
Right now each is configured entirely independently. What is the right way to remotely manage a device and how does that affect how we use encryption?

https://github.com/uProxy/uproxy/issues/550
https://github.com/uProxy/uproxy/issues/700

 Comments: 
 Comment 0: #702 

 Comment 1: Marking this as P1 for web store launch - not because I think we necessarily need to change anything, but because we should come to some consensus around this before going forward as it might be a pain to change our minds later.

 Comment 2: With the ability to cryptographically pair devices, we'll want to be able to manage these paired devices remotely

 Comment 3: Moving this to the 2.0 milestone as it shouldn't block public launch (coming up very very soon!).  We will probably be making changes to permissions (sharing permissions users rather than devices) in https://github.com/uProxy/uproxy/issues/1014, but other features dealing with cryptographic identity will be handled in a later milestone. 

Also for remote device management (e.g. changing my laptop uProxy settings from my desktop), the current best answer is that uProxy users should use a remote window manager like Chrome Remote Desktop
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