Append(l1):Insert(l2) Hidden(l1):Hidden(l2)
- foobar_l2 should be directly to the left of artist
- foobar_l1 should be on the far right
- both foobar_l1 and foobar_l2 should be in the column picker for this page
- neither foobar_l1 or foobar_l2 should be in the column picker for the main library
- BUG: neither splitter around l1 is resizable