TermIt

As a developer, I want to implement a generic messaging UI, which would put messages (like "Save successful" etc.) into a queue and display them as popups/notifications.

Acceptance criteria:
- A global message queue is available in the UI for components/actions.
- Messages added to the queue are displayed in a dedicated overlay component.
- Messages have automatic TTL. When it expires, the message is dismissed.
- Messages can be dismissed manually by clicking on a close button.
- A predefined number of messages is displayed at once. If there are more messages, they wait in the queue until an empty display slot is available (their TTL counts since the moment they are displayed).
- Tested.