Added SceneObject Children and Transform unit tests.
Refactored SceneObject Children functions.
Refactored SceneObject constructor which takes a parent to add the SceneObject as a child of that parent.
Updated tests accordingly.
Added tests for SceneObject Key and Mouse events.
Changed SceneObject onMouseMove parameters from int to float.
Adding const to some getter functions and changed Scene to require a non-null root node during construction
Added include guards to test hpp files
Added blank Scene test file for later