Merge pull request #2501 from ProjectMirador/window-prop

__tests__/src/components/CompanionArea.test.js

__tests__/src/components/ErrorDialog.test.js

__tests__/src/components/WindowList.test.js

__tests__/src/components/Workspace.test.js

__tests__/src/components/WorkspaceMosaic.test.js

__tests__/src/selectors/windows.test.js

src/components/CompanionArea.js

src/components/ErrorDialog.js

src/components/WindowList.js

src/components/Workspace.js

src/components/WorkspaceMosaic.js

src/containers/CompanionArea.js

src/containers/ErrorDialog.js

src/containers/WindowList.js

src/containers/WindowSideBarButtons.js

src/containers/Workspace.js

src/containers/WorkspaceMosaic.js

src/state/selectors/windows.js