* Extend dropzone widget with optional actions invoked after tm-import-tiddlers message has been sent. Allows triggering an alternative UX for the import
* Allow restricting a dropzone to specific mimeTypes via mimeTypes and mimeTypesPrefix attributes
* Use a mimeTypesFilter instead of the mimeTypes and mimeTypesPrefix attributes
* Updated refresh handling
* Syntax cleanup
* Replace references to mimeType with content type for consistency with existing documentation. Update documentation for DropZone widget