Dismiss notification should hide directly

[PVince81]

Steps

1. Have some notifications present under the bell icon
2. Open notifications dropdown
3. Click the cross icon to dismiss a notification

Expected result

Notification disappears directly.

Actual result

Delay of 1-2 seconds until it disappears.

For a better UX, we should hide the notification right away even if the XHR call is still ongoing. Worst case we can still re-display it in case of an error.

[PVince81]

adding "help wanted" / junior job as the fix should be a matter of quick rewiring

[nickvergessen]

I think before this it needs to be migrated to a proper vue store and have a way back, because currently it just removes the element from the local array and I don't know how it would revert that.