Allow multiple definitions of DMF attributes

[wixoaGit]

A DMF or winset with duplicate keys will use the last value. This fixes dark mode in Nebula, since their winsets define each attribute twice:

winset(src, "output", "background-color = none;background-color = [COLOR_DARKMODE_DARKBACKGROUND]")
winset(src, "output", "text-color = #000000;text-color = [COLOR_DARKMODE_TEXT]")

I also changed some of the more spammy console logs to be Verbose.