Allow Support for Custom Color Palettes

[Kully]

It would be very useful to allow the possibility to use your own color palettes. And if this is possible, we would need to come up with a pragmatic and easy way to allow a user to import their colors (eg. maybe copy and paste HEX colors into a text field).

@Kully is already working on a solution for this. Here's a screenshot of the current WIP (branch and Pull Request will eventually come)