PaletteDialog: replace apply with restore defaults

[pvmm]

Now the palette editor allows the user to restore palette to the default MSX palette. Apply is not as useful as the Defaults button, so it was removed to reduce clutter.

[m9710797]

Hi,

This PR is fine. I'll merge it.
I do have one remark, but it's about the existing code, not about your changes:

BitMapViewer and TileViewer each have a global variable 'currentPalette'. In general global (non-const) variables should be avoided. So maybe these should be made member variables of the BitMapViewer/TileViewer classes?

I also wonder why BitMapViewer and TileViewer each have their own 'currentPalette' array, Maybe this should be a shared array? (Because even if you use a custom palette rather than the current VDP palette, I assume it's useful to have the same custom palette between BitMapViewer and TileViewer)

[pvmm]

I also wonder why BitMapViewer and TileViewer each have their own 'currentPalette' array, Maybe this should be a shared array? (Because even if you use a custom palette rather than the current VDP palette, I assume it's useful to have the same custom palette between BitMapViewer and TileViewer)

Then maybe store it in VDPDataStore and call it alternativePalette.