Group migration: maintain import status across reloads

After implementing new import status approach, we've discovered that ATM we do not provide to frontend enough import status info to recover proper mapping of available import groups and pending imports. At the moment if user leaves or refreshes page - all group import statuses will be lost

Proposed solution

As intermediate solution, we are going to persist initiated imports in local storage, allowing user to leave/refresh page and to see import status when coming back

Illustrations

The UI mockups can be found here: #271505 (closed)