Refactor POST handling.

- Split into admin and user handlers, each admin page gets its own file now
- Enforce role access once for admin POST requests
- Automatically load POST logic for admin-based requests based on the referring page, otherwise automatically load all user request logic
- Add support for using custom POST handlers

post/ai.php

@@ -4,6 +4,8 @@
  * ITFlow - GET/POST request handler for AI Functions
  */
 
+// TODO: Should this be moved to AJAX?
+
 if (isset($_GET['ai_reword'])) {
 
     header('Content-Type: application/json');
@@ -54,4 +56,4 @@ if (isset($_GET['ai_reword'])) {
         echo json_encode(['rewordedText' => 'Failed to get a response from the OpenAI API.']);
     }
 
-}
+}