Update v1.040 (Heroes)

This update introduces heroes into the game who give an little extra help to each level when used. Currently, there are two different heroes, each a set of skills that are unlocked by gaining experience and leveling up.

The soldier can use a concussion grenade to daze monsters temporarily.

The engineer can buff towers temporally making them much more powerful.

Please note that the heroes are not final and things will change in the near future. The interface for hero selection is a prototype and will be overhauled soon but I wanted to get a testing version out so I can get feedback on the heroes!