Game Mechanics Updated

There have been some changes and updates to the some of the game mechanics. Here is a short summary of the changes.

• Added a "level failed" mechanic that allows you to stage before landing and continue to the next level, having failed the objective of that level. Failing 3 levels will result in a game over.
  
• A framework has been added to allow multiple game modes to be implemented. Unimplemented game modes will have their respective buttons grayed-out.
  
• A thrust-to-weight ratio indicator has been added to the upgrades screen to determine if you need to increase engine power. The ascent stage's TWR is the first number while the descent stage's TWR is the second number.
  
• A basic subsystem damage system has been implemented, allowing certain parts of the vehicle to be disabled without triggering a crash condition.
  

• New button graphics.
  
• Staging before landing no longer results in being stranded.
  
• Giving contradictory control inputs will result in them being canceled-out. All button and axis inputs for a specific control are added together with the response that you get being the sum of all of the inputs.
  
• All features that are not yet implemented have had their controls grayed-out.
  

• Fixed a bug where the center of mass is not at the vehicle's local origin. This caused an issue with the orbit script not calculating the vehicle's position correctly.