add api control of file drop handling behavior

src/kiri/init.js

@@ -1004,6 +1004,13 @@
 
         let files = evt.dataTransfer.files;
 
+        switch (API.feature.drop_group) {
+            case true:
+                return API.platform.load_files(files, []);
+            case false:
+                return API.platform.load_files(files, undefined);
+        }
+
         function ck_group() {
             if (files.length === 1) {
                 API.platform.load_files(files);

src/kiri/main.js

@@ -70,7 +70,8 @@
 
     const feature = {
         seed: true,
-        controls: true
+        controls: true,
+        drop_group: undefined
     };
 
     const selection = {