Support float color in picker module
The picker module reports colors back in RGB 8 bit. This is completely uncommon in high end image editing. What is used are float values from 0..1. Furthermore, the picker should display true values. I.e. when loading a HDR image or a DNG with values outside the 0..1 range, the picker should display these correctly to e.g. aid with picking a correct exposure + highlight reconstruction (if the latter ever works well enough).