* split play-button into container and component
* revised sound library tile:
  * play button in upper right
  * smaller sound icon (make the tile less loaded)

Play button doesn’t have a ‘touch-outside’ listener to stop sounds. That seems to be ok as other events cause the sound to stop.

Both handleClick and handleMouseDown are needed. Must use handleMouseDown for `preventDefault` to skip setting focus on the item. handleClick is needed to prevent the Click from propagating to the item and selecting it.

Update UI play/stop button when the sound ends

Play button is larger (easier to touch). Can both start and stop sounds.
Sound doesn’t restart on mouseEnter if the sound is already playing.
Sound stops if you move off play button

Missing: stop button does not revert to play button when the sound finishes.

Add prop to library items to show a play button. If a play button is present the ‘play on hover’ only applies over the icon rather than the full tile.

* add scratchLogo as default for logo prop
* prefer `{featureAllowed && (<Component />)} over ternary operator with a null ‘else’
* renamed `handleSaveToComputer` as `getSaveToComputerHandler` to more clearly represent what it’s doing (returning a function to be the handler)
* renamed the parameter that is the function to handle clicking on the load project menu item (also updated the comments in `SBFileUploader`)

This reverts commit c061f2e2, reversing
changes made to 6e007b1e.

Comments slightly tweaked from kchadha's suggestions

Co-Authored-By: Karishma Chadha <kchadha@media.mit.edu>

Because the video steps get replaced by an image step if offline, we should not show items that would result in having no content