demo projects: support "PIC24F DA/Color Depth"

InternalResourceColorDepth_8BPPMode*.xml contain errors: .bmp instead of
.gpl is used as palette path, but it doesn't matter because it doesn't
cause an error and the palette is taken from the XC16 precompiled
source anyway.
SDL: support palette with 1 or 4 bpp color depth

There was no difference between using LSB or MSB pixel format.
Color Depth demo: switch to 4 bpp

There is already a demo with 8 bpp palette.
Color Depth demo: preparation for setting to 1 bpp

The filename is different.