Restore original context menu ordering

Previously I used CSS specificity to order the most specific / recently
added menu items for a given element *first* when building up the
context menu. When a duplicate label was found for a given menu I would
refrain from inserting it. Now instead I order things the opposite way.
The most specific / recently added items come later and items with the
same label are clobbered by later items.
Put platform items back on .overlayer so they sort before package items