- 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

package.json

@@ -10,7 +10,7 @@
     "test": "test"
   },
   "engines": {
-    "node": ">= 7.6.0"
+    "node": ">= 8.5.0"
   },
   "scripts": {
     "prepublishOnly": "npm run test-prep",