Gametype-configurable player trails

[Gelmo]

Gametypes and gametype configs should be able to specify the following in regard to player trails:

• Whether or not player trails should be shown at all
  • Someone implementing a custom gametype may want to disable player trails globally (even for teammates), even if the player has player trails enabled via the cvar
• Whether or not opponent trails should be shown
  • In a bomb match, for example, you'll want to see teammate trails but opponent trails probably shouldn't be shown, for competitive integrity. Same with duel and TDM, perhaps
• The speed threshold for showing trails
  • In some gametypes (instagib, futsball), the server admin may want to show trails for all players, and they may want those trails to be drawn at all speeds rather than just high speeds

This assumes that you'll always be able to see teammate trails, which can be disabled globally by the player via the cvar. I think this approach is more suitable than hardcoded values either globally or per gametype. Allowing it to be configured by server admins is a must.