Allow QtC Quick Designer to have Color Swatches

QtC Quick Designer is clearly set in a path to become a Designers' Tool for creating great UI's.

Swatches are very useful for creating palletes for any specific project. If, say QtC remembers last colors or allows for easily remembering colors and palletes (or swatches) it will greatly benefit designers.

A simple option to store ~10 colors and a button "Add to my colors" is a basic and useful implementation. We can store it in the QtC Session.