Add a button to make the workspace fullscreen; fixes #1702

__tests__/src/actions/workspace.test.js

__tests__/src/components/App.test.js

...sts__/src/components/WorkspaceControlPanelButtons.test.js

__tests__/src/components/WorkspaceFullScreenButton.test.js

__tests__/src/reducers/workspace.test.js

package.json

src/action-types.js

src/actions/index.js

src/actions/workspace.js

src/components/App.js

src/components/WorkspaceControlPanel.js

src/components/WorkspaceControlPanelButtons.js

src/components/WorkspaceFullScreenButton.js

src/reducers/workspace.js