add support for switching Hub users

[unitycoder]

this file contains current login token:
C:\Users%USERNAME%\AppData\Roaming\UnityHub\encryptedTokens.json

if you delete it, next time hub starts, you are logged out.
if you switch it to another valid encryptedTokens.json data, you are logged in as that user.

• add settings button to manage your tokens (grab current login token, assign name to it?)
• add settings button to switch user somehow (dropdown with your names?)
• add button to delete your tokens (if they become invalid?)
• need to restart hub, when user is changed? or would unity editor use new token if started after switch?
• problem: hub asks to activate license after switching token (maybe this activation data is saved somewhere?)
• problem: requires admin access to modify that tokens file (need to launch some command to do the switch and then it asks for permissions?)

BUT, if user wants to automatically use correct login PER project, it would need to save that info inside UserSettings/ folder?
and them pick that username to load tokens..