Improve usability of the mini color dialog

[caesay]

I have recently implemented a mini-color-picker in the experimental branch. This issue is to track some potential improvements.

• [ ] Keyboard support (eg. Enter, Esc)
• [ ] Remember recently used custom colors as a third swatch row. Store in global settings.
• [ ] Allow you to switch between HEX, RGB, and HSL textbox modes similar to the devtools implementation
• [x] Apply color changes in real time and remove the "Cancel" and "Accept" buttons at the bottom.
• [ ] Eye dropper to pick a color from screen

[rstarkov]

Color picker "accept color" de-selects the current tool. It shouldn't.