pad.html: UI telling the user that a contribution is required before importing

This commit is an integration to 24ee37a38f.

src/static/js/pad_editbar.js

@@ -394,6 +394,17 @@ var padeditbar = (function()
 
     toolbar.registerCommand("import_export", function () {
       toolbar.toggleDropDown("import_export", function(){
+
+        if (clientVars.thisUserHasEditedThisPad) {
+          // the user has edited this pad historically or in this session
+          $('#importform').show();
+          $('#importmessagepermission').hide();
+        } else {
+          // this is the first time this user visits this pad
+          $('#importform').hide();
+          $('#importmessagepermission').show();
+        }
+
         // If Import file input exists then focus on it..
         if($('#importfileinput').length !== 0){
           setTimeout(function(){