added some method definitions for handlers
Input Update 1

Added relationship between KeyInputHandler and UserAirplane
Removing unnecesary class: ImageLoader

Class: ImageLoader.java

has been replaced by

Class: Assets.java
Update plannedClassStructure
made some initial changes to how airplane/ship handle turning and moving
Removed GameTickHandler from constructor and created a
setGameTickHandler. Right now, this function stores the GameTickHandler
and then calls the register function to add the entity to the list.

Also, cleaned up code from my last commit a bit.
Added some commenting. Moved many of the shared functions and variables
in AAirplane and AShip to the AShootingEntity class.
Cosmetic changes
Graphics and Game Screen

Added code for draw() to Airplane, Ship, and Projectile
Started the game screen just needs a way to push update and draw to
objects
Merge Screen Package

Deleted separate Screen source folder
Updated GTH and GameScreen

Added GTH to gamescreen