Some stuff which doesn't get clocked by .gitignore..

It annoys me to see that I have files to commit. I'm working on my own here anyway so I can commit them without any huge problem.
Changed Wall constructor..

Changed from (..., ..., Vector2 halfSize) to (..., ..., Vector2 bottomRight).
So now you have to give Wall the topLeft and bottomRight corners.
Added Draw to QuadTree for debugging.
Added the QuadTree debugging in GameplayScreen..

The debugging is set to false for now.
Inserted a click algorithm for inserting items to the QuadTree which is commentoud out of the code right now. Will be used later for debugging the QuadTree.