+ Added Gun Reload Sound (For every 4 shots)
+ Reorganized the code so it fits more into a 'GameLoop design pattern'

Things that need to happen:
- 1) RandomEnemyGenerator method in the GameLoop class has to be
'converted' into a 'factory' method
- 2) To number one, we will need to remove the switch-case statement and
make use XML
- 3) We need to figure out how to use XML and implement a functionality
that is able to load details about units (enemies) using XML