Notifications improvements

[m-orlova]

Introduce jmix-notification component that supports:

1. Dedicated areas for title,body and footer
2. title,body and footer can be either component or text
3. Markdown text (same as vaadin-tooltip) - body only
4. prefix and suffix slots
5. Close button
6. Modality like a dialog
7. Click on notification (and backdrop) closes it. Configurable.
8. title and footer are optional
9. Same API as vaadin-notification
10. Notifications bean - Notifications.Type assumes default icon (prefix)

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Original issue as motivation

Currently, there is no easy way to show a notification with icon and simple text or title+description. Need to use custom component each time or override Notifications bean to used such notifications by default.

Example of notifications:

It will be useful:

1. Have API in notifications for adding icons.
   Example:

     notifications.create("Unable to execute operaion")
                           .withType(Notifications.Type.ERROR)
                           .withIcon(VaadinIcon.WARNING.create()) // also it can be a custom icon
                           .build();
   

2. Configure usage of icons in notifications by default instead of adding each time