Convert commerce_checkout_pane_info to array

Committed. I did have to switch the merge order of saved values into checkout panes... previously we were using array_merge() but for some reason tucked a + operator in there so that the array_merge() wasn't actually doing anything. Fixing this resulted in a flipped merge order, so saved values weren't loading properly... discovered this when testing a page with its default panes disabled... the page was still showing up even though the panes weren't.