Weapon / item pickups, plus old art and code.

I migrated my old Unreal 4.2 prototype over.  There are a lot of good assets in here to start incorporating. 

• Moved the generated weapons over to the game instance so that they are still there between levels.
• Added weapon pickups generation to the city level.
• Added a projectile hit effect (explosion / particle system).  Doesn't seem to trigger on the space station objects for some reason, but works on other objects. Strange bug.