Fix Scrutinizer issues in mod [_well_know -> contactgroup]

- Remove unused variables and parameter
- Updated function documentation
- Fix formatting
- Add back uninitialized variables
- Simplify nested conditions

src/Core/Config.php

@@ -130,7 +130,7 @@ class Config
 	 *
 	 * @param string $family The category of the configuration value
 	 * @param string $key    The configuration key to set
-	 * @param string $value  The value to store
+	 * @param mixed  $value  The value to store
 	 *
 	 * @return mixed Stored $value or false if the database update failed
 	 */