When the DataImport instance for the current user has the show_alert flag set to false, the view does not display the alert related to OPML imports.

This change has required adding the show_alert flag to the set of values that are returned in the JSON for the DataImport.
The DataImport alert in the start page can now be permanently dismissed when the import status is ERROR or SUCCESS.
The DataImport alert in the start page cannot be dismissed while the import is running.
Added tooltip to the close button in the DataImport alert displayed in the start page.