Feature request: Import and Export palettized bmp and png formats

[mrgudenheim]

Feature request to allow importing and exporting .bmp and .png files with 4-bit or 8-bit bit palletized format that includes palette data for up to 256 colors. When importing there would be a way to import the entire palette including colors that are not used in the image or to selectively overwrite the existing palette with colors from the imported file (similar to how GraphicsGale does it). When exporting, a user could choose the 8-bit per pixel (8bpp) or 4-bit (4bpp) bmp or png format to include the current palette in the file data.