gnu: breeze: Split from breeze-icons.

gnu: breeze: Split from breeze-icons.

KDE breeze is separate from breeze-icons, as it can bee seen by
version, download path and git repository path being all different.
Thus a package containing both beeze and the breeze-icons contradicts
with this upstream separation.

* gnu/package/kde.scm (breeze-assets): Remove variable. (breeze): Move to ...
* gnu/package/kde-plasme.scm (breeze): here.
  [version, source]: Copy from former breeze-assets.
  [build-system]: Make explicit (was inherited even from breeze-icons).
  [arguments]: Remove.
  [native-inputs]: New element.
  [inputs]: Copy from former breeze-assets; add some optional packages.
  [home-page]: Fix and change to invent.kde.org.
  [snopysis, description]: Adjust to de-unified package.
  [licence]: Remove gpl3+, which came from breeze-icons.