Notification list view.

[farmaazon]

What should work from the user perspective

On the right-top corner of the scene, there should be a bell icon: clicking on it should show the notification list. The notifications should be HTML boxes with a short message, displayed along the right edge of the scene, sorted from newest to oldest. User should be able to remove notification from the list. Clicking again should hide the notification list.

There are four kinds of notifications: process, event, error, and warnings. Notifications of different kinds are displayed with different background color. Processes are removed from the list when some process is finished (e.g. compiling stdlib) without user intervention.

If a new notification arrives and the list is hidden, the bell icon should be in "unread" state. This state is removed once the user will show the notification list.

The user should see the notifications we currently display in the "status bar" (i.e. warning about unsupported engine version, compiling standard library process, error about losing connection).

The look of the notifications can be quite plain, there is another task for improving it. Scrolling notification is also not in the scope of this task.

How it should be implemented

The API for controllers to push new notifications should be like those in StatusBarView, but with new notification kinds.

As the EnsoGL text area does not handle multiline text well, the notification boxes should be displayed as DOM divs.
Only the visible notifications shall be rendered.

[farmaazon]

The tasks for #5201 should be redesigned for new GUI