[Approved] Plasma 6 proposal: Make window titlebars accent colored by default

If someone wants to go ahead and implement this, feel free to; I likely won't get around to it anytime soon.

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Linking up on #74 (closed), I would like to propose to turn on the "Make window titlebars accent colored" option for our Breeze themes by default. This is not only eye candy, but also helps accessibility. Compare how much more difficult it is to tell which window has focus with our current gray as opposed to the active window being highlighted in the accent color:

Initial proposal:

before	after

Current proposal (to be discussed):

before	after
(same as above)