Change talents panel to allow artistic background

[arnvid]

I think you can put a ticking option to allow the Talents panel skinning or not depending of the person's preferences (if it's not too much additional work & stuff of course), but yeah the Talent background defaut panel from Blizzard is already quite good tbf, with Aurora re-skinning only like the title bar, it's great enough that way I find!

Originally posted by @Heregellas in #150