|SOURCE|
[Common::GUI]
* This class is responsible for managing the GUI elements in the program
* RenderDebugOverlay will iterate over all GUI elements and draw their debug
  representations
* SetRenderer verifies the renderer being passed in is valid (not null) before
  setting the local renderer to it
[Common::GUIElement]
* Added a Colour struct to allow for GUI elements to have some colour to
  represent them (this should be moved to a more generic header file)
* Added SetDebugOutlineColour to set the colour to be used when debugging this
  GUI element
* Added GetDebugOutlineColour for the GUI class to extract the colour to use
  when rendering this element for debugging
* The default debug colour is set to white with full opacity in the constructor