Allow widgets with a name-spaced `uiType`

Defaults to widgets in the `ui` namespace to keep backwards compatibility. e.g. `uiType: 'droppable'` will still work.

Allow a widget with namespace to function e.g. [blueimp.fileupload](https://github.com/blueimp/jQuery-File-Upload) will work via `uiType: 'blueimp.fileupload'`.