- Fix: Ensure PHP files are present in dist/extensions alongside JavaScript files using them

- Fix: Bug in obtaining `extPath` in ext-server_opensave.js
- Enhancement: Add config `avoidClientSide` to avoid using client-side support by default (and always require server)
- Build: Require Node 8.5

dist/extensions/allowedMimeTypes.php

@@ -0,0 +1,12 @@
+<?php
+
+$allowedMimeTypesBySuffix = array(
+  'svg' => 'image/svg+xml;charset=UTF-8',
+  'png' => 'image/png',
+  'jpeg' => 'image/jpeg',
+  'bmp' => 'image/bmp',
+  'webp' => 'image/webp',
+  'pdf' => 'application/pdf'
+);
+
+?>