MLA glue: support external memory

Emulate external memory via ExternalMemoryCallback() interface if
USE_PALETTE_EXTERNAL, USE_FONT_EXTERNAL or USE_BITMAP_EXTERNAL are used.
The memory content is embedded in the executable.
demo projects: support "External Memory"

Programming the external flash not implemented, it is "preprogrammed".
Color Depth demo: support external memory for bitmaps, fonts and palettes

Can be used by defining EXTERNAL_MEMORY in the build system.
Set individual window titles for the example and demo projects

Fall back to "MLAtor" if MLATOR_WINDOW_TITLE is not defined.