Show a Progress Bar when Importing/Exporting XML Backup

Comment from customer:

"This is not a problem, merely a suggestion for future updates if possible. We performed a migration last night of our JIRA database from V3.6.5 to V4.1.2 and found that when backing up the data to zip file and also when restoring the data, there is no indication on the screen how these activities are progressing. When you re-index the data you are presented with a progress bar which gives you an idea of how far the activity is progressing whereas with backup and restore activities you are left with nothing to indicate how it is progressing."

So, show a Progress Bar when Importing/Exporting XML Backup.