Improve Page Restriction design to give feedback while sub-pages are put into the index queue

Queuing of the items to re-index of pages with lots of children is done on the requesting thread. In some cases this can take so long that the browser times out (ex. IE times out after 2 minutes). An information message should be presented to the user that this operation will take some time. A progressbar should be shown to indicate that work is being done and allows the user to track the changes. The actual work will therefore need to happen on a separate thread.