--Latte should remember 300 backgrounds
maximum and afterwards that cache is removed.
That way we can avoid cases that because
a slideshow plugin uses too many wallpapers
does not make Latte to have high memory usage.
--the luminas functions didnt work well
for all cases. Latte is now using brightness
functions as described at:
https://www.w3.org/TR/AERT/#color-contrast
this patch fixes all cases mentioned in the bug
that Latte contrast identification did not work well
BUG: 402115
Michail Vourlakos