Move to PropTypes for React 15.5

package.json

src/components/asset-panel/selector.jsx

src/components/blocks/blocks.jsx

src/components/box/box.jsx

src/components/close-button/close-button.jsx

src/components/costume-canvas/costume-canvas.jsx

src/components/green-flag/green-flag.jsx

src/components/gui/gui.jsx

src/components/library-item/library-item.jsx

src/components/library/library.jsx

src/components/modal/modal.jsx

src/components/sprite-info/sprite-info.jsx

src/components/sprite-selector-item/sprite-selector-item.jsx

src/components/sprite-selector/sprite-selector.jsx

src/components/stage-selector/stage-selector.jsx

src/components/stage/stage.jsx

src/components/stop-all/stop-all.jsx

src/components/target-pane/target-pane.jsx

src/containers/backdrop-library.jsx

src/containers/blocks.jsx