Including sprites, backdrops, costumes and sounds inputs

I needed to update the player css because the editor side wasn't large enough to be useable.

Update project changes test to test a project change that should actually emit a change event. Clicking on blocks should not emit a project changed event.

I know we will want to change this eventually, so I added comments about that. But the next commit originally contained an inadvertent change to this functionality, so I wanted to add an integration test so that when we do change it, we

It looks like an "test.only" was left in on one of these tests by mistake.

Adds unit tests for this HOC.

Forcing the playhead onto its own painting layer removes an expensive composite with the waveform. Animate using transforms instead of left prevents layouts of the rest of the page while playing a sound.