Splash screen/options menu

[jackson-57]

There should be a splash screen and an advanced options menu, that should:

• Explain the purpose of the website
• Recommend to the user to set their devices to output 720p (which looks significantly better than 1080p)
• Show the control scheme (eg. the fullscreen keybind)
• Show the selected video and audio devices, and allow the user to override them
• Show the resolution, frame rate, and (if possible) the color format, and allow the user to override them
• Allow the user to disable stereo audio conversion (and show the current audio format?)
• Allow the user to disable audio or video entirely (?)