Thanks @ericrosenbaum!

Fix issue with sound upload button not always working, and correctly cache sound type if given an mp3.

There's a subtle difference in behavior between mouseup and click. Using mouseup allows you to close the menu by clicking its opener item.

whoops

It's shifted downward to not overlap the menubar, since it's hard to make a child z-indexed below its parent.

It's a cleaner API IMO but ended up being a messy implementation...