Move Breeze to Framework

[Nate Graham]

A long term concern I have is that it's messy and unpleasant to have 
default styling data scattered across so many places. Ideally we'd be 
able to centralize *all* data about a particular style in a single repo, 
so that making changes is easy and that repo can be swapped out for 
another one in the future.

I see an opportunity to move closer to that here. So my preference would 
be to implement the proposal, but also:
- the default window decorations remain in Breeze
- the default colors remain in Breeze, and are removed from KColorScheme
- breeze-icons is merged into Breeze

Then later we can investigate what it might take to haul the 
Plasma-scoped Breeze visual theming (e.g splash screen, SDDM theme, 
Plasma SVG theme) into that repo as well. But that can be a longer term 
thing.

Nate