update v41.1

The Military Base is one of the last theme of Modern Exteriors and will feature tons of new buildings, vehicles and props

- Added an Helicopter (back-view)
- Working on a propeller animation 

- See you and happy game-making! :)

The new theme is only available in the "WIP_Theme".zip until it's finished.  This way you won't have to download the whole asset to just have a couple of new sprites.