api: import from commento export format

JSON data can be imported to restore previously exported data
or to migrate data from another self-hosted commento instance.

Closes https://gitlab.com/commento/commento/issues/239

frontend/js/dashboard-import.js

@@ -34,4 +34,29 @@
     });
   }
 
+  global.importCommento = function() {
+    var url = $("#commento-url").val();
+    var data = global.dashboard.$data;
+
+    var json = {
+      "ownerToken": global.cookieGet("commentoOwnerToken"),
+      "domain": data.domains[data.cd].domain,
+      "url": url,
+    }
+
+    global.buttonDisable("#commento-import-button");
+    global.post(global.origin + "/api/domain/import/commento", json, function(resp) {
+      global.buttonEnable("#commento-import-button");
+
+      if (!resp.success) {
+        global.globalErrorShow(resp.message);
+        return;
+      }
+
+      $("#commento-import-button").hide();
+
+      global.globalOKShow("Imported " + resp.numImported + " comments!");
+    });
+  }
+
 } (window.commento, document));