Update dependencies

With jscodeshift thank God

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# Conflicts:
#	package.json

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# Conflicts:
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# Conflicts:
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Closes #311

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Closes #288

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Use sprite info for costumes and sounds

Standardize settings

* Set editing target when double clicking on sprite in stage

* rename double clicker handler and add comment

These dependencies are only needed by `npm run clean` and (indirectly)
`npm run build` which only work when the other dev dependencies are
installed.

Fix dragging sprite only when mousedown starts on sprite

Use `rimraf` and `mkdirp` instead of `rm -rf` and `mkdir -p`.

Add missing file types to `.gitattributes`.
Use `node` instead of deprecated `stable` version specifier for Travis.
Set dev tool to `cheap-module-source-map`.

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