Great thanks for the update thi3r!!
Just to clarify for anyone else coming up with the same issue - the latest branch of GridFieldBulkEditing tools has had the file GridFieldBulkEditingTools.php removed and therefore the class GridFieldBulkEditingTools (which is referenced in the Gallery module in GalleryPage.php) no longer exists. Simply uncommenting the line in GalleryPage.php seems to have fixed the issue.