Dropping plasma 5 version due to limitations porting foreground colorization

[luisbocanegra]

It seems the ability to override icon colors is only available in plasma 6 KDE/ksvg@50c5716

But for Plasma 5 only alternative I can think of is using ColorOverlay/Colorize from QtGraphicalEffects but the results don't look very good, icons and text get blurry and it supposedly has a performance impact.

Additionally that would make the implementations diverge and will make maintenance of both versions more difficult and I would like to just focus on the latest Plasma version.

For those reasons the plasma 5 port won't be maintained anymore.