Create admin users and web setup

[IRHM]

Currently all users have the same basic permissions and there isn't a way to make a certain user an admin.

For #137 we will need to know which users are admins.

On a new install, we need a small setup process so the server owner can make the first admin account.

For existing installs, we will probably have to create a page, which will log a code into the server console (expire after 5m), which can be used to set the current account as an admin. This should be the easiest way for getting admin after updating.

• Generate json config file on startup
• Read json config and update code to use these instead of old environment vars
  • JWT_SECRET
  • JELLYFIN_HOST
  • SIGNUP_ENABLED
  • TMDB_KEY
  • DEBUG
  • MODE (staying as env var, but not through .env file, but rather set through cli when starting)
• Create admin users (and simple setup page)

[IRHM]

Config needs manual editing still until #137