Importing Sounds - Selection Easier and Clearer

[maryfries]

Hi! Me (with the teachers in Cleveland) again!

A teacher just tried to import a built-in sound, did /almost/ everything right, but then didn't get anything imported. They clicked play on a bunch of sounds until they found one they liked and then clicked import, but they didn't realize that they hadn't selected a sound.

From my perspective, there were two things about Snap that could be improved here:

1. It should be more visually clear which/whether a sound is selected
2. Snap should automatically select whichever sound was played last