Improved notifications cleaning UI with set operations (#109)

* added notification cleaning drawer

* bugfix

* fully implemented set operations for notif cleaning

* i18n for notif cleaning drawer & improved logic slightly. Also added a confirm dialog

* - notif dismiss "overlay" now shoves the notif aside to avoid overlap
- added focus ring to header buttons
- removed notif overlay entirely from DOM if mode is disabled

* removed comment

* CSS tuning - inconsistent division lines fix

app/javascript/glitch/components/notification/overlay/container.js

@@ -43,7 +43,7 @@ const mapDispatchToProps = dispatch => ({
 });
 
 const mapStateToProps = state => ({
-  revealed: state.getIn(['notifications', 'cleaningMode']),
+  show: state.getIn(['notifications', 'cleaningMode']),
 });
 
 export default connect(mapStateToProps, mapDispatchToProps)(NotificationOverlay);