When loading an asset, construct the URL not by using the default data
type of the type of asset being loaded, but the actual data type of the
skeleton asset passed in. This allows the asset requestor to override
the data format, for example when loading a JPEG-format backdrop.

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.

With jscodeshift thank God

Attaching the storage module in `vmListenerHOC` means it can propagate
down to the GUI, stage, and blocks naturally. The default VM property
value has been removed from those places so that we're not instantiating
extra VM instances any more. Instead, using one of those components
outside of the `vmListenerHOC` framework will require providing a VM
instance as a property.

Remove target pane button and actions

Add back putting the sound library in the ui

There are a handful of places where the GUI code could use the storage
module directly; converting those is for a later change.

* Update blocks.js

Fixes #220