Refactored to fix an issue where the EMP blast wasn't being created.

Brief outline here, refer to commit messages on Bitbucket for more details.

• Added spin out mechanic: DARs spin out and explode when decapitated.
  
• Added hover mechanic: DARs hover below the ceiling.
  
• Improved flight AI behaviour, including checks for whether flying is appropriate.
  
• Fixed DARs orbiting around path nodes and players' heads.
  
• Added more powerful spawn replacement system for flying DARs.
  
• Added support for Endless mode.
  
• Rebalanced DARs: reduced speed, health, armour and damage. However, they spawn more frequently now.
  
• Goliath body and armour health now scales with players.
  
• Adjusted the appearance of the stinger and goliath (draw scale and burnt/frozen visual effects).
  
• Majorly refactored code - any mods that use the previous flight code will need overhaul integration code to use the new code. It should be easier to extend now.
  
• Added replication and simulation for multiplayer (still needs work, particularly for spin out rotation).

Alpha clots are no longer replaced by bombers on wave 1. It was a bit too hard.