Add-ons Alert Improvements by Xon 2.10.13

• Another attempt to reduce deadlocks during alert pruning
• When editing a post, mark related alerts as read, as this displays changes in post contents to the visitor
• If Live Content add-on is installed; only try to mark alerts as read if the visitor has unread alerts

• Reduce possibility of deadlocks when pruning alert cleanup table
• Fix summary alert pagination

• Add CLI command "xf-rebuild:sv-alert-totals" to expose rebuilding alert totals job
• Avoid updating alerts which are condinates to be pruned, this should reduce the possibility of the alerts cleanup tasks generating deadlocks