Further refinements on 5cp mode

A series of changes to make 5cp mode more consequence-based and less
random, including:

- Revert HUD elements to standard 5cp HUD.
- Both teams spawn at mid.
- The result of the midfight determines which team's second the next
  fight will take place at.
- Teams only scramble after capturing the opposing team's last.
- Make backcaps take longer.
- Disable First Blood in 5cp mode.
- Automatically set tf_caplinear to 0 in 5cp mode, but revert to 1 in
  any other mode.
- 30 second timer after a respawn capture resets the gamestate to the
  way it was at the start of the round, encouraging fast pushes.
- Hide models of the team_control_points not in play.