Now the remap is calculated from the old palette to the new palette when
the "Remap" button is pressed. In this way we can remap after loading
a new palette (fix#737), or after generating an optimized palette, or
changing colors (fix#563).
This commit includes the new doc::PalettePicks class. It's a helper
class to identify which entries are selected in the ColorBar.
We've removed the Copy/Paste buttons from the Palette Editor window.