Rework Notifications: separate and bundle to an amount of 4 (#13300)

* WIP notifications only show 2 at once

* separate and bundle notifications to pairs

* notification fadein/-out/move animations - remove notifications on an interval instead of calculated timeouts

* easier way to import all sprite css files

* add stories + fix sizes / paddings + click to hide + animation fixes

* keep notification at the top but always under the toolbars

* change animations to ease-in 0.25s + add prop to change the delay between deletion and add

* fix adding logic in a rare case of added notifications when only one item is currently visible + add debug mode

* disable lint for notification console

* add more notification example trigger buttons

* potential fix of animation / queue

* increase amount of notifications to 4

* fix sanity

* fix test:unit call again

* new notification styles - fix animations

* keep error notifications visible until manually removed + refactor adding/removal logic

* fix margins

* prevent multiple filling + different delay on filling

* stop and restart removal timer on new notifications

* reduce line-height / apply different margin for icons

* move sprites.scss out and use it in app.vue as well

* update sprites back to 31

website/common/script/libs/sleepAsync.js

@@ -0,0 +1,5 @@
+export function sleepAsync (ms) {
+  return new Promise(resolve => {
+    setTimeout(resolve, ms);
+  });
+}