Server-side recording and admin spectator system

[Chomenor]

This adds basic server-side recording support, enabled by sv_recordAutoRecording 1. Recorded files can be converted to the standard dm_68 demo format for playback. It also allows admins to spectate the server without joining, enabled by setting sv_adminSpectatorPassword, which can be useful to monitor for cheating.

I expect this should generally work with any mods that are compatible with client-side demos, but if any compatibility issues do come up they probably shouldn't be hard to fix.

Current limitations / features which could be added later:

• No built-in compression; currently post-compressing record files with zip or 7z reduces size by ~2x-3x.
• No free-movement spectating.
• No direct playback of .rec files. Must be converted to demo before playing.

[Chomenor]

I think this should be safe to merge, as it shouldn't have any effects unless enabled by cvar. I can help support it with fixes and improvements in the future. If there is interest I might be able to add Q3SDC-like live replay support.

Feel free to let me know if you have any questions or changes to request.