#4 #2 Implemented sprite movement on screen with keyboard arrow input

Added an update_position method to cPosition_component so the movement
system can update entity locations

Moved input handling into the game manager.  An array of boolean values
determines if a key is currently pressed.  Events and key presses are
handled in cGame_Manager.handle_input.  When a certain key is pressed,
the appropriate movement system call is made

Movement system has methods for specifically altering an entity
position such as key_up or key_down
The movement system will also operate on objects with contstant
velocities that need updating