Gallery discoverability in Play Sound block

[Jaqster]

Lower priority as we didn't see a majority of students having this problem, but a couple of them from the usability study couldn't find the Gallery tab in the Play Sound block field editor. We may want to see if we can increase discoverability by making the Editor Gallery toggle shorter and maybe with a thicker outline to look more like a clickable area in the Field editor. Look at Play Melody block for inspiration -