Support switching Plex users on an authorized server

[chrisbenincasa]

We had a report from a user who wanted to be able to switch to a specific user on their server.

High-level investigation shows that we should be able to list users with:

https://clients.plex.tv/api/home/users

The 'protected' bit here indicates whether the switch step will need a PIN

And then switch to the new user and get a new token with:

https://clients.plex.tv/api/v2/home/users/USER_ID/switch

This is a POST request with headers like 'pin', etc.

One complication here is if a user already had content and then switches their token to a user who does not have access to the content already added. This could lead to a really weird experience... we could pop a warning if the user tries to switch users after adding content, or something similar