[ERM-11] Improve the resulting notification message

[smiakchilo]

As a Rollout Manager user, I need to receive an extended notification upon the finish of the rollout process.
The notification should include:

• the number of pages that have been rolled out
• the list the pages for which the rollout failed, specified by paths.

If the rollout was requested for a parent page with children, the notification should contain info about either the parent or every child page (== all pages are reported "independently").

The notification should be properly positioned on the screen regardless of the list of pages (== it should have fixed height and contain and internal scrollable container).

Note: implementation might depend on the integration of the "live feedpack" solution, such as EToolbox Contractor -- see #16