New GDISP image handling with demo

Images currently support Native and BMP (except RLE4,8 and 16 bit - due
to bugs)
Supports reading from Memory, BaseFileStream or real files (only on the
Win32 simulator).

Move gdisp_pictures demo to better refect its purpose.

Bug fixes for BMP RLE4,8 & 16 bit to come very soon
GIF support very soon.