access already chosen colorvalues in colorpickers

[b3nson]

in form of:

• copy/paste colorvalues from one picker to another or
• show colorvalues of other pickers
• retain a list of last used colorvalues

...

[b3nson]

Done. Not yet perfect:

• How to handle RGBA-values in RGB-colorpickers correctly?!
• Programmatically set colorvalues (e.g. bgcolor on startup) sometimes differ from colorpicker set values. Inaccuracy in conversion from value to slider-positions?!