Added XTENTO to partners list (#60)

* Added XTENTO to partners list

XTENTO will continue providing support for M1/OpenMage in the longterm.

* Added XTENTO logo to module vendors directory

* Update module_vendor.json

Author: ikk0

_data/partners/module_vendor.json

@@ -1,4 +1,11 @@
 [
+  {
+    "name": "XTENTO",
+    "url": "https://www.xtento.com",
+    "description": "Flexible. Stable. Trusted by thousands of merchants. XTENTO provides Magento 1 and Magento 2 extensions mainly in the import/export space and is known for its great customer support.",
+    "img_src": "/assets/images/module-vendors/xtento-logo.png",
+    "classes": "xtento"
+  },
   {
     "name": "RedChamps",
     "url": "https://redchamps.com",