Added login UI

[Zentro]

This will add the ability to log into your Rigs of Rods account from inside the game. This replaces the "user token" system currently in place with something that requires much less hassle.

How to test:
At the very top of the main screen, click "Login". Enter your forum credentials and if prompted test each two-factor option. Make sure your login and refresh token are set.

Currently, the login dialog box works along with the additional two-factor steps.

• Migrate our databases to DO managed databases services
• Get the XF addon production ready
• Push changes to carbon (the API), will be accessible from https://v2.api.rigsofrods.org/auth
• Download user avatars into a cache
• Logout and clear user avatar cache
• Update RoR server to allow a 2 way key exchange for ranked users (gutting the user token system)

I've attached an older video for demonstration.

1.mp4

[ohlidalp]

Code looks perfect from my perspective 👏