Show status Dialog for open / import folder action

1) Adds a SparkActionWithStatusDialog abstraction to show status dialogs for blocking actions.
2) Show a status dialog for Add Folder, Import folder.

@ussuri PTAL thanks.
@dinhviethoa  `_selectFolder` opens a folder picker. I had to pass the `action` here, because we don't want to show the status dialog, if the folder picker is cancelled. Same reason applies for comments below.