For those of you who needs Pantone colors support in Affinity Designer before the Serif team release an official support in it, here is a trick you can do.
Firstly, you need an Adobe Illustrator licence to be able to do this, or install a demo version of Illustrator.
Then you need to install SwatchBooker.
http://www.selapa.net/swatchbooker/
Or you compile it yourself to get a Mac version, or you use it under Linux, or use it with Windows.
Personally, I installed the Windows version into a CrossOver bottle and it works out of the box.
Launch SwatchBooker Editor, in the File menu, select Open and choose one of your Pantone library in Illustrator.
Then in the File menu, select Save as and select *.ase for the file format.
Launch Affinity Designer and go to the swatches panel, click on the menu and choose import palette, as system or software, as you want. Select your exported *.ase color library.
And that's it, you have loaded in Affiinty Designer your Pantone colors library.