1.67 released

1. Added and enabled contest functionality.
2. Server crash bugfix.
3. Bugfix in dogfight score.
4. Bugfix in replay path.
5. Bugfix in editor load map.
6. Added support for per level gravity and "air" resistance.
7. Levels can have horizontal gravity.
8. Added mission_hard, mission_coop3, race00_zero, race04_jupiter, mission04_mod, mission06_mod.
9. Many minor enhancements.
10. Major project files update (compiles for x64 and mac).
11. Fix in pathes used in Linux.