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/tag_model.php

@@ -1,5 +0,0 @@
-<?php
-$name = sanitizeInput($_POST['name']);
-$type = intval($_POST['type']);
-$color = sanitizeInput($_POST['color']);
-$icon = preg_replace("/[^0-9a-zA-Z-]/", "", sanitizeInput($_POST['icon']));