Merge branch 'develop' into monitors

package.json

src/components/asset-panel/selector.jsx

src/components/button/button.css

src/components/button/button.jsx

src/components/load-button/load-button.css

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

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

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

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

src/containers/costume-tab.jsx

src/containers/load-button.jsx

src/containers/save-button.jsx

src/containers/sprite-selector-item.jsx

src/containers/stage-selector.jsx

src/lib/vm-listener-hoc.jsx

src/reducers/gui.js

src/reducers/targets.js

src/reducers/vm.js