Add isRequired to required prop types

src/components/asset-panel/selector.jsx

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

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

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

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

src/components/library/library.jsx

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

src/containers/costume-tab.jsx

src/containers/sound-tab.jsx