Tests for Load Scenes, fixed/added enemy class tests, add reward ability when destroy the center tower

[hongjiehuang]

I have added some tests to Load Scenes, and now when the player destroy the center tower, he will get a ability to use. I did not have a chance to add more tests, I will try to write more tests and documentations after the final.

[RyanLinrm]

I'll also catch up with the tests and documentation after the exam, I've add getting score on board, I'll try to modify your destorying center tower code to assign score to the user, Thank you, Jay