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/user/network_model.php

@@ -0,0 +1,13 @@
+<?php
+$name = sanitizeInput($_POST['name']);
+$description = sanitizeInput($_POST['description']);
+$vlan = intval($_POST['vlan']);
+$network = sanitizeInput($_POST['network']);
+$subnet = sanitizeInput($_POST['subnet']);
+$gateway = sanitizeInput($_POST['gateway']);
+$primary_dns = sanitizeInput($_POST['primary_dns']);
+$secondary_dns = sanitizeInput($_POST['secondary_dns']);
+$dhcp_range = sanitizeInput($_POST['dhcp_range']);
+$notes = sanitizeInput($_POST['notes']);
+$location_id = intval($_POST['location']);
+$client_id = intval($_POST['client_id']);