Migrate away from PlasmaCore.ColorScope

Everything that was ColorScope now is in Kirigami.Theme

SvgItem and FrameSvgItem also don't need a colorGroup to be manually
set,
they already follow the Kirigami.Theme.colorSet

The couple of replacements of IconItem to Kirigami.Icon needed to get rid of colorscope already there are ok as are the standard icon components of buttons and such, for which the icons from the system icon theme are already ok.