Fixed bug: clicking Preview button causes Save button to open in a new browser window when clicked.
Instead of being configurable, made xhr_paging always enabled.

This option made no sense to be turned off because it makes for a better
user experience to prevent a full page reload when paging.
Merge pull request #2733 from refinery/enable-xhr-paging-by-default

Instead of being configurable, made xhr_paging always enabled.