Okay, I kept plugging and found out what to do. It turns out I can "Hide" a category:
by right-clicking and choosing the option (if I Exclude it, that's bad). Which gives me this:
Hopefully I can figure out how to un-Hide something, but that's another story.
NOTE: If anybody does find out how to put the gridlines in FRONT, I would still like to know.
I have this same question! Has anyone figured out how to put grid lines in front of bars yet? Thanks!