Thanks @paulkaplan

This reduces the complexity of the reducer, as well as how frequently it's run. The VM will emit a targets update after a step if any target info has changed.

Otherwise it's very annoying to get access to the storage engine to load asset data.

Remove target pane button and actions

Add back putting the sound library in the ui

These aren't necessary to update in realtime, so throttle them to once every 30ms

Add a new stage selection component that displays the stage separately from the sprite list.

In preparation to split the sprites from the stage, start managing the target list state in a single place.