Enable "Save now" menu item when there's a session

package.json

src/.eslintrc.js

src/components/menu-bar/menu-bar.css

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

src/containers/backpack.jsx

src/containers/gui.jsx

src/containers/project-saver.jsx

src/lib/project-loader-hoc.jsx

src/lib/storage.js

src/reducers/gui.js

src/reducers/project-id.js