Add support for locally stored user profiles

[valereandota]

Users can be stored locally on the device, potentially a dictionary linked to the user e-mail.
Example : { user_email: [saved schedules, refresh token, auto-signup(bool), course_colors, ... ],user_email2: [saved schedules, refresh token, auto-signup(bool), course colors, ... }
Preferences then become local user specific and will be locally stored allowing for quick swapping of accounts on the same device.
This will allow multiple accounts from different schools or similar on a single device.