Level 3, with Laser and Sprinter

Added a new level (3rd) in the latest update. It comes with a new enemy - Sprinter - which moves faster than others. It's difficult to catch it with slow aiming Gun and Canon. To deal with it a new tower is added - Laser. A laser can deliver damage at a higher rate, therefore it's perfect to deal with Sprinters. Laser costs same as a Canon. It's somewhat ineffective against shield.

Also added a new escape menu, to pause game and then resume/reload a level.