Add colour settings for active/inactive title bar blend colours

These are still used by KDE2 and some other window decorations.

Use "Secondary" instead of "Blend" as suggested in review.
Also reorder the items so that the 3 "Active" settings come
together, followed by the 3 "Inactive" settings.

BUG:225837
REVIEW:100821
FIXED_IN:4.7.0
GUI:
I18N: