Add-ons Alert Improvements by Xon 2.13.0

• Fix incorrect phrase for default alert type in admincp
• Fix new alert types could be opted out by default instead of opt-in
• Fix user's alert preferences may not save with some configurations
• On alert opt-out list; only render "reset" checkbox for non-default values

• Fix setting "Alerts page skips summarizing" in "User Registration" to false wasn't applied to new accounts

• Fixes for grouped/summarized alerts
  • Group by newest alert not oldest when computing alert summary data
  • When gluing together per-content type reaction summary, use ", " not just whitespace.