Merge pull request #1816 from ProjectMirador/1774-toggle-zoom-controls

__tests__/src/actions/workspace.test.js

__tests__/src/components/WorkspaceMenu.test.js

__tests__/src/components/ZoomControls.test.js

__tests__/src/reducers/workspace.test.js

locales/en/translation.json

src/components/OpenSeadragonViewer.js

src/components/WorkspaceMenu.js

src/components/ZoomControls.js

src/containers/WorkspaceMenu.js

src/containers/ZoomControls.js

src/state/actions/action-types.js

src/state/actions/workspace.js

src/state/reducers/workspace.js