Slightly rounder elements for more friendly feel

I felt like since we're in Plasma 6 now, maybe the Breeze theme could use teeny tiny facelift.

Only couple things have been changed:

• Frame radius from 3 to 5
  • The effect is subtle, but I think it makes Plasma look friendlier
• Update window decoration to similar values
• Context menus have same roundness as window decorations
  • Them being different has bothered me :D

Before:

Dark	Light

After (ignore any differences with outlines):

Dark	Light

Check teams/vdg/issues#45 (closed) for full task list