House keeping

- Remove the potentially GPL-infringing discord_pass.h file.
- Let DISCORD_APPID be a public #define.
- Use server_context as party ID.
- Add more states ("Watching Demo", "Menu").
- Only show map images on supported maps. Falls back to an image of a dice.
- Displays "???" as the map name for Hell maps.
- Voting displays an image of the BG planet, depending on the gamemode.
- Added a fallback title screen large image.
- Added a fallback character image.
- General code cleanup & safety checks.
- Give CV_NETVAR to cv_maxplayers (I should come up with a better way of sending this information without overwriting user settings, but this'll do for now)