Added a basic X11 window

|SOURCE|
[Common/Window]
* Added a WINDOW_RECT struct member variable for derived classes to use
[Linux/X11Window]
* A basic window is created based on the WINDOW_RECT passed into Initialise
* The Git version information is displayed in the centre of the window
[Linux/Main]
* A window is created at location 0,0, with a width of 1024 and a height of 768
  pixels