We now initialize/destroy the display in Xlib::init/shutdown that is called in UnixApplication::init/shutdown and
therefore is valid through the whole lifetime. So no need for classes to keep references.
source/Graphics/Image/IcoFormat.cpp: use new PixelFormat.
source/Graphics/Image.cpp: update to confirm with new PixelFormat
Spectre/Graphics/PixelFormat: add PF_getNumChannels()
Spectre/Graphics/PixelFormat: Rework the enum with proper naming convention and documentation.
