fix: move debug mode to config (#3324)

* fix: move debug mode to config

* fix: also move debug_whitelist to .ini config

* fix: move logic back to Debug class

* docs

* docs

* fix: disable debug mode by default

* fix: restore previous behavior for alerts

* fix: center-align alert text

docs/04_For_Developers/05_Debug_mode.md

@@ -5,23 +5,29 @@ Enabling debug mode on a public server may result in malicious clients retrievin
 ***
 
 Debug mode enables error reporting and prevents loading data from the cache (data is still written to the cache).
-To enable debug mode, create a file named 'DEBUG' in the root directory of RSS-Bridge (next to `index.php`). For further security, insert your IP address in the file. You can add multiple addresses, one per line.
+To enable debug mode, set in `config.ini.php`:
+
+    enable_debug_mode = true
+
+Allow only explicit ip addresses:
+
+    debug_mode_whitelist[] = 127.0.0.1
+    debug_mode_whitelist[] = 192.168.1.10
 
 _Notice_:
 
 * An empty file enables debug mode for anyone!
 * The bridge whitelist still applies! (debug mode does **not** enable all bridges)
 
-RSS-Bridge will give you a visual feedback when debug mode is enabled:
-
-![twitter bridge](../images/debug_mode.png)
+RSS-Bridge will give you a visual feedback when debug mode is enabled.
 
 While debug mode is active, RSS-Bridge will write additional data to your servers `error.log`.
 
 Debug mode is controlled by the static class `Debug`. It provides three core functions:
 
-`Debug::isEnabled()`: Returns `true` if debug mode is enabled.
-`Debug::isSecure()`: Returns `true` if your client is on the debug whitelist.
-`Debug::log($message)`: Adds a message to `error.log`. It takes one parameter, which can be anything. For example: `Debug::log('Hello World!');`
+* `Debug::isEnabled()`: Returns `true` if debug mode is enabled.
+* `Debug::log($message)`: Adds a message to `error.log`. It takes one parameter, which can be anything.
+
+Example: `Debug::log('Hello World!');`
 
 **Notice**: `Debug::log($message)` calls `Debug::isEnabled()` internally. You don't have to do that manually.