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/ticket_recurring_model.php

@@ -0,0 +1,23 @@
+<?php
+
+$client_id = intval($_POST['client']);
+$subject = sanitizeInput($_POST['subject']);
+$priority = sanitizeInput($_POST['priority']);
+$details = mysqli_real_escape_string($mysqli, $_POST['details']);
+$frequency = sanitizeInput($_POST['frequency']);
+$billable = intval($_POST['billable']);
+
+$asset_id = "0";
+if (isset($_POST['asset'])) {
+    $asset_id = intval($_POST['asset']);
+}
+
+$contact_id = "0";
+if (isset($_POST['contact'])) {
+    $contact_id = intval($_POST['contact']);
+}
+
+$assigned_to = "0";
+if (isset($_POST['assigned_to'])) {
+    $assigned_to = intval($_POST['assigned_to']);
+}