Add OSD-internal state information to the workspace state; fixes #1644

__tests__/src/actions/canvas.test.js

__tests__/src/components/OpenSeadragonViewer.test.js

__tests__/src/reducers/windows.test.js

src/components/OpenSeadragonViewer.js

src/containers/OpenSeadragonViewer.js

src/containers/Workspace.js

src/state/actions/action-types.js

src/state/actions/canvas.js

src/state/reducers/windows.js