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.

Checked with Carl and updated the style of the play button.

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.

Update scratch-vm to the latest version 

Update scratch-vm to the latest version 

Remove test.only

Update chromedriver to the latest version 

Greenkeeper/scratch blocks 0.1.0 prerelease.1564581595

Update fade icons

Prevent default when dragging trim handles to prevent image drag

Do not update trimmers only if both have not changed

Closes #5034

Sound editor update: selection-based editing

Roll forward scratch-svg-renderer