Add import/export rules and fix lint errors

package.json

src/.eslintrc.js

src/components/asset-panel/asset-panel.jsx

src/components/asset-panel/selector.jsx

src/components/audio-trimmer/audio-trimmer.jsx

src/components/blocks/blocks.jsx

src/components/box/box.jsx

src/components/buffered-input/buffered-input.jsx

src/components/button/button.jsx

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

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

src/components/filter/filter.jsx

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

src/components/gui/gui.jsx

src/components/language-selector/language-selector.jsx

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

src/components/library/library.jsx

src/components/load-button/load-button.jsx

src/components/menu-bar/menu-bar.jsx

src/components/meter/meter.jsx