[Feature] Micheal Zhou's GSoC palette branch got merged

[Wolthera]

While Micheal hadn't had much time to poke at it last week, boud and I
took a look at it, getting some last details out.

We've decided it's stable enough for testing and surely more stable
than my own crashy palette code, so it is being merged!

New features include:
1. Instead of an entry-based docker, a rows and column based docker.
2. It can hold empty entries, which is useful for organizing.
3. Stable drag and dropping of colors.
4. Easy adding in entries by clicking them in the docker.
Right-clicking removes an entry.
5. Palettes can be put into the kra file. You can press the folder
icon to open a palette editing dialog where you can set a palette to
be stored in the document or resource-folder.

And generally it's a lot more stable. Please try it out so we can
polish it even further! :)

-- 
Wolthera