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()

config.json.example

@@ -0,0 +1,32 @@
+{
+    "site_title": "CodePress",
+    "content_dir": "content",
+    "templates_dir": "cms/templates",
+    "active_theme": "default",
+    "default_page": "auto",
+    "language": {
+        "default": "nl",
+        "available": [
+            "nl",
+            "en"
+        ]
+    },
+    "seo": {
+        "description": "CodePress CMS - Lightweight file-based content management system",
+        "keywords": "cms, php, content management, file-based"
+    },
+    "author": {
+        "name": "E. Noorlander",
+        "website": "https://noorlander.info"
+    },
+    "show_version": true,
+    "enabled_plugins": [
+        "MQTTTracker",
+        "HTMLBlock"
+    ],
+    "features": {
+        "auto_link_pages": true,
+        "search_enabled": true,
+        "breadcrumbs_enabled": true
+    }
+}