* Set editing target when double clicking on sprite in stage

* rename double clicker handler and add comment

Fix dragging sprite only when mousedown starts on sprite

Fix audio images in sounds tab

* Fix costume loading in sprite info pane

Requires LLK/scratch-vm#517

* Fix costume loading in costumes tab

Requires LLK/scratch-vm#517

Use decodeSound and scratch storage for loading sounds

Use backdrop library in costume tab

* chore(package): update autoprefixer to version 6.7.7

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* chore(package): update css-loader to version 0.28.0

Closes #231

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* chore(package): update postcss-simple-vars to version 3.1.0

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* chore(package): update react-modal to version 1.7.3

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* chore(package): update react-style-proptype to version 2.0.2

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# Conflicts:
#	package.json

* chore(package): update style-loader to version 0.16.1

Closes #253

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* chore(package): update webpack to version 2.3.2

Closes #264

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Fix backdrop and costume loading from libraries

Stricter PropType validation

Change #off to #removeListener

Use scratch-storage

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.

Tabbed sound and costume panels

Sound library first iteration

Remove target pane button and actions

Add back putting the sound library in the ui

Fix block editor borders 

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

Fixes #156 + refactored classnames to style guide conventions

Affects SpriteSelector Pane, StageSelector Pane, Stage, MenuBar, Libraries Modal, Add/Import buttons, for Chrome, Ffx + Safari on Sierra.

Fixes #162

Add simple blocks background pattern