Add system update feature, git-ignore local configs, and fix homepage request logging

- Exclude config.json and admin.json in .gitignore so live settings/passwords are never overwritten by git
- Auto-generate config.json and admin.json with defaults if missing
- Add config.json.example and admin.json.example reference templates
- Add System Update page (/admin/update) in Admin Console to pull updates via Git with 1 click
- Log effective page name in index.php instead of literal 'auto'
- Add extra HAProxy/PFSense proxy headers to RequestLogger::getClientIp()

cms/core/class/RequestLogger.php

@@ -29,6 +29,8 @@ class RequestLogger
             'HTTP_CF_CONNECTING_IP',
             'HTTP_X_REAL_IP',
             'HTTP_CLIENT_IP',
+            'HTTP_X_CLIENT_IP',
+            'HTTP_X_CLUSTER_CLIENT_IP',
             'HTTP_X_FORWARDED_FOR',
             'HTTP_X_FORWARDED',
             'HTTP_FORWARDED_FOR',